Oil light comes on once temp gauge is up to normal.

Are you running oil of proper viscosity for temperatures in your area?

Both issues could be normal to a degree. The engine temp would go up some when the truck stops moving, and the oil pressure would go down some when the engine returns to idle.
Are the two gauges reading out of normal range ?

Possible bad sending unit or shorted sending unit wiring.

You may or may not have a problem with the fan. It should come on around 220 degrees or when the ac is running.
The temp on the gauge and the temp the computer sees can be 10 or 15 degrees different either way.

It could be a plugged heater core or heater control problem. I assume the blower is working, but the air is cold. The first thing to check is the coolant level, make sure there is coolant in the resivoir. Next see if the temerature gauge reaches the normal operating temperature range. If the gauge reads cold most of the time, it would tell you that the thermsotat is faulty and not allowing the engine to reach full operating temperature. If your car doesn't have a temp gauge, the blue cold engine light might stay on for an extended period of time. The thermostat is supposed to not allow coolant flow in the radiator until the engine reaches operating temperature. If you drive the car for a couple of minutes, from cold start, the radiator or upper hose should be cool until the engine reaches operating temp.

Hi,

The overheating and lack of cabin heat both point to a failed engine thermostat which would be stuck closed. At the warm up stage, the coolant stays in the engine block to bring the engine to efficient operating temperature, then it opens and circulates the coolant through the radiator and heat core. If the thermostat is stuck closed, the engine will overheat, and coolant will never reach the heater core, and you will not get cabin heat.

Blinking oil light at idle which goes away during driving could be a low oil level, but may also be a drop in oil pressue. You could have a clogged oil fliter (at best) pickup tube, or a failing oil pump.

I would suspect either the temp guage or the coolant temperature sensor being inaccurate. The new thermostat is probably working good, or else you wouldn't have a very warm heater. If you have electric radiator fans, you might check to see if they are running all th time. Electric cooling fans should only come on when the temperature sensor reaches a predetermined coolant temp, or when the a/c or defroster is turned on. If the fan runs all the time, the engine would not reach normal operating temperature.

you should switch the temperature sensor and oil pressure sensor you had on your first engine,because your new engine must come with the light indicator dashboard so the sensor of your new engine are not compatible with your gauges....lipak!...

Could be the oil pressure sender has gone bad or worse case scenario the oil pump has worn out. Check the oil presssure sender first, if it is leaking around it then that is the cause, if not then you may be looking at an oil pump. Just had a 03 ram 2500 doing the same thing and it was the sender, but that was a hemi and it had 230000 miles and a month later had to replace the oil pump for same issue.

It's overheating.  check thermostat and water pump, also radiator coolant levels.  once you get it running at normal temp again take it to the shop and have them do a chemical test to see if the head gasket was damaged or the block was warped or cracked as this usually happens when your car overheats.