Replaced head gaskets upper lower intake gaskets now wont start 96 vortec

Intake manifold-to-cylinder head bolts....96 in-lbs
Intake manifold, upper to lower bolts ....132 in-lbs

Tighten all bolts from center of manifold towards the ends.

You have to reove the upper plenum. that is the part on top of the intake that looks like a dome on top of the lower intake.There is 8 10mm bolts around the outside of the dome part. the disconnect the fuel lines at back of lower intake and remove the cpi unit.

this does sound like a head problem (hopefully just the gasket). pulling the head with the exhaust manifold attached is possible but tricky and difficult. risking the bolt and drilling it out if it snaps would be alot easier. I would strongly suggest having the head checked while its off (so you dont rebuild to find that you wasted time and money on a bad head)

The website has software that looks for obscene words.
I would think a compression test would show if the cylinder is having mechanical problems. And yes the intake or head gasket could be leaking again, especially if the intake or head were warped or cracked.
Have you checked fuel pressure ?
Does the spark plug for cylinder 5 show signs of coolant leaking into the cylinder ?

Sounds like it could either have bad head or head gaskets.

To install:

1. Clean all gasket surfaces completely.
2. Install the intake manifold gaskets with the port blocking plates facing the rear of the engine. Factory gaskets should have the words "This Side Up" visible.
3. Apply gasket sealer to the front and rear sealing surfaces of the engine block.
4. Apply a 0.197 inch (5mm) bead of RTV sealer to the front and rear of the block. Extend the sealer approximately 1 / 2 -inch (13mm) onto the heads.
5. Install the lower intake manifold.
6. Apply sealer to the lower intake manifold bolts prior to installation.
7. Install the bolts and tighten in sequence and in 3 steps as follows:
   1. First step to 26 inch lbs. (3 Nm).
   2. Second step to 106 inch lbs. (12 Nm).
   3. Final step to 11 ft. lbs. (15 Nm).
   
   
8. If removed, install the alternator bracket bolt.
9. Install the coolant by-pass hose.
10. Install the EGR valve.
11. Connect the upper radiator hose to the thermostat housing.
12. Connect the heater hose to the lower intake manifold.
13. Connect the fuel pressure and return lines to the lower intake manifold.
14. Connect the wiring harnesses and brackets to the lower manifold.
15. Install the throttle cable bracket, then attach the throttle cable and the cruise control cable (if equipped).
16. Install the transmission oil level indicator and tube, if equipped.
17. Install the EGR tube, clamp and bolt.
18. Install the PCV valve and hose.
19. Install the A/C compressor and bracket.
20. Install the distributor.
21. Install the upper intake manifold.
22. Fill the cooling system.
23. Connect the negative battery cable.
24. Start the vehicle and check the ignition timing (not adjustable).
25. Verify no oil, coolant, vacuum or fuel leaks.

    

26. Install the intake manifold bolts and tighten them to 35 ft. lbs. (48 Nm) in the sequence shown.
    

you will have to remove upper intake plenum the black plastic part there is a o-ring around the area you are speaking of. now if this engine didn,t have the intake gaskets replaced before installing now would be good time because if you keep vehicle believe me you will have to do sooner or later these engines came with plastic intake gaskets that are notorious for leaking to do this you will njeed to remove both upper and lower intake manifolds I just started a job on 99 tahoe today before lunch and customer is driving tonight replaced upper and lower intake gaskets fel-pro makes updated gaskets for this engine that has thick metal shim and rubber gaskets a great improvement that ends this problem as for your vacuum leak at opening for fuel lines don,t see often but is possible hope this helps

If your going to replace the lower intake and the set came with the upper why not replace it, your removing it any way.the silicone you need to used it at the 4 corners where the heads meet the engine block or you will have leaks.

3.8L Engine

NOTE The 3.8L (VIN K) non-supercharged engine uses a two-piece intake manifold consisting of an upper air plenum which mounts the throttle body and a lower intake manifold assembly which houses the fuel injectors. The 3.8L (VIN 1) supercharged engine uses a similar lower intake manifold. The supercharger serves as the upper manifold.
Lower Manifold

NOTE Two bolts which fasten the lower intake manifold to the cylinder head are accessible only after the upper intake manifold is removed. These bolts are located in the right front and left rear corners of the lower intake manifold. Remove the upper intake manifold to service the lower intake.
The 3.8L (VIN 1) supercharged engine uses a manifold similar to the 3.8L (VIN K), but the supercharger serves as the upper manifold.

1. Disconnect the negative battery cable.
2. On 3.8L (VIN 1) engines, remove the supercharger assembly. Please see the procedure in this section.
3. Remove the upper intake manifold using the procedure above.
4. Remove the EGR outlet pipe from the intake manifold.
5. Detach the engine coolant temperature sensor wiring harness from the sensor.
6. Remove the lower intake manifold bolts and carefully lift off the manifold.

To install:


Fig. Lower intake manifold bolt torque sequence-3.8L (VIN K) engine

1. Clean all parts well with degreaser, especially the gasket seal surfaces on the upper and lower manifold pieces and between the lower manifold and the cylinder heads..
2. Install new gaskets to the cylinder heads and new seals to the engine block. Carefully lower the manifold into place. Apply thread-locking compound to the bolt threads. Make sure to install the two hidden bolts in the lower intake manifold. Hand start all bolts, then torque evenly to 11 ft. lbs. (15 Nm). Follow the toque sequence, starting in the center, then working outwards in a circle.
3. Install the remaining components in the reverse order of the removal process.

Upper Intake Manifold (Plenum)

1. Disconnect the negative battery cable.
2. On 3.8L (VIN 1) engines, remove the supercharger assembly. Please see the procedure in this section.
3. Tag for identification, then remove the right side spark plug wires.
4. Disconnect the ignition wires from the fuel rail.
5. Remove the fuel rail. Please see Section 5.
6. Remove the cable bracket from the intake manifold.
7. Remove the throttle body.

NOTE Two bolts which fasten the lower intake manifold to the cylinder head are accessible are accessible only after the upper intake manifold is removed. These bolts are located in the right front and left rear corners of the lower intake manifold.

1. Remove the upper intake manifold bolts and carefully lift the upper intake manifold from the engine.

Fig. Upper intake manifold and bolt torque sequence-3.8L (VIN K) engine
To install:

1. Clean all parts well with degreaser, especially the gasket seal surfaces on the upper and lower manifold pieces.
2. Install new gaskets to the cylinder heads and new seals to the engine block. Carefully lower the manifold into place. Make sure to install the two hidden bolts in the lower intake manifold. Hand start all bolts, then torque evenly to 89 inch lbs. (10 Nm). Follow the torque sequence, starting in the center, then working outwards in a circle.
3. Install the remaining components in the reverse order of the removal process.

It sounds like the upper section (known as the plenum) of the intake may be leaking at the gasket, this is a common problem on a 5.0L V8. It takes about 1-2 hours to change, and the gasket is cheap, make sure that you throughly clean the gasket surface of the upper and lower intake before putting it back togeather, you will need a special tool to remove the center Torx head retainning bolt, it is a long star/torx bit, It is a T40 The MAC tool number is SC161.