Code 63, 31,32 hard codes, 12v at tps reference, 4.8v at egr reference. computer has been change, but do not know if it is correct one for truck. i have vin and number from computer if there is a way to match up.

Did you change the TPS (Throttle position sensor)?

Several things can cause the engine power to be reduced. Yes, the EGR valve can affect and reduce the engines power if it is stuck open (even just partially). The valve must be in the closed position. and will open as the ECU decides to. P2138 can refer to the TPS but can also refer to the throttle pedal. Is the throttle pedal electric or does it have a cable? If it is electric then you also would need to inspect TAC unit. I hope this helps. If you have more information and or details please let me know. Good luck.

code p0403 refers to EGR --circuit malfunction===causes ---wiring--EGR solenoid---ECM
code p0405 refers to EGR valve position sensor A --low input===causes ---wiring ---short to ground---EGRF valve position sensor--- ECM.
By only changing the EGR valve you have not fixed the problems that cause the valve not to work.

Code 122 is for a low signal from the TPS, and code 405 is for a low signal from the EGR position sensor. The computer sends a 9 volt signal to most of the sensors and the return signal tells the computer what is happening.
For example, if most of the 9 volt signal comes back from the TPS the computer knows the throttle is closed.
I would check the two circuits to see if the reference voltage is there. If it is not, it could be a problem in the harness, or inside the computer.

code p1120 refers tothrottle position sensor1--circuit malfunction---causes ---wiring open cuircuit--/short circuit to ground/short circuit to positive---throttlecontrol unit---ECM
code p0401 refers to exhaust gas recirculation(EGR) valve system---insufficient flow detected. ---causes hose leak/blockage--basic setting not carried out (if applicable)---wiring---EGR valve---EGR solenoid----ECM. I would replace the EGR valve for starters Get unit from the wreckers. You may have to have the CPu reset with a code reader tool

No royal purple wont hurt your car, in fact it is a really good oil. and yes your egr will cause a lot of problems, including the ones you are describing

the egr could be the problem if its not working correctly,,,

31 canister or egr valve control system,63 throttle position sensor or circuit,for egr inspect visually hoses elect. plug at egr solenoids after that you might want to buy a repair manual because theres quite a few test to do.for tps check unplug connector at sensor connect 1probe of dig.ohmmeter to center terminal the other on either side move throttle slowly,resistance should vary slowly,if its erratic or none change tps ,voltage at plug not sure,think its 5vlt

Given that you have replaced the TPS and the PCM, the next step would be to check the connector itself and make sure it is making a good connection and there are no corrosion or anything like that on the connector.

After that, ensure that the TPS has the correct voltage to it, usually its around 5vdc, it should never have full batter voltage to it (12vdc). The PCM usually supplies both the 5vdc reference and the ground for the TPS. Its also entirely possible that (depending on where you bought the TPS) that you were given the wrong one for your vehicle. Not a common thing, but it could happen.

The code will be set if the PCM sees a TPS angle that is not consistent with the RPMs of the engine. If you are having any shifting issues such as hard shifts or the engine having to rev higher to shift, that usually a clear indication there is still something wrong with the TPS circuit even if the TPS itself is good.

Hope this helps.

the 3.1 had some EGR problems, EGR valve stuck open, blown diaphrams, Plugged passages Im not saying that is all your problems and I believe yours has whats called a linear EGR about $350.00 from the dealer (and that is the only place you ever consider buying such a critical part for the emissions system regardless of the cost)
That car is so antiquated as far as computers go that relying on the codes is nearly pointless! Map code can set because of low engine vacuum which you will have with a poor running engine, Check for 5 volt reference voltage at the TPS and MAP with the key on and engine off if no 5 volt reference I suspect a Computer. Computer Ground is on the Thermostat housing and needs to be clean and secure.
There is a legit test in the GM factory manual called the TAP TEST take the ECM (computer) and slap it with an open hand, if the symptoms change the ECM is bad it's very common in the early-mid 90s for the computers to go bad in one way or another the circuit boards come loose and suffer also from cold solder joints.
Make sure the wires are on the correct plugs and hopefuly you used factory plugs and wires and No split fire or bosch plugs only AC delco
Make sure you have good spark on all 6 cylinders.
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