GMC Repair: Oil pressure falling, chevy 350, high mileage

Question
Hi
I have a 1988 chevy truck, it has a TBI chevy 350 in it.

Very recently had the heads done, and i even replaced a piston and rings. High mileage motor.

I also replaced the oil pump with a brand new one.

The oil pressure was always strong, all the way up to the 60 psi mark all the time.

I changed the oil, i use 10w40, and Lukas oil additive.

I then had to drive my truck back to school, which is about 160 miles. It was fine at first, but then about half way through i noticed it started to drop, to about 45 or 50. Then by the time i got to school it had gone up to 60 again.

After driving it some more to stores, it kept dropping, to around 30 psi. Today i drove for about 45 min, and i couldnt even keep it at 30, it got all the way down to 15 psi. It never gets up to 60 anymore.

Even when it is around 15 psi, i will floor the truck, and it makes no difference.

All of this changed when i did an oil change.

DO you have any ideas of what it could be?

thanks

kolby semrow

Answer
it sounds like you may have gotten a bad pump. also pull the distributor and check the gear on the bottom. Make sure that the roll pin is still in tact. It sits in the drive shaft for the oil pump. If it looks worn. replace it. and you may be told that it is unlikely that the oil pump is bad. However, I have experienced that new parts can be bad. We have received such parts several times.