I would appreciate opinions you all might have on my very strange oil
pressure problem with my TJ
97TJ
2.5L
4-Speed
A/C

Just had oil change, filter (FRAM PH16), tail pipe/muffler, ac charge,
front disc pads, serpentine belt.

Works fine on short hops. Oil gauge stays on 40  just like always.
After I go about 10 miles, when I some to a stop the oil pressure
drops little by little, but goes right up to 40 when I rev the engine.
Eventually, it will fo down low enough to trigger the oil light but
all I have to do is hit the gas and I'm fine.

Oil level is ok - full, no frothl. No leaks anywhere. I don't know
where the oil pump is so I can't see if it's loose but I'd suspect
that if it was, there'd be oil everywhere. Valve cover cap is on
tight.

The only other new noises or symptoms is:  
- Then I start up, the new S belt screeches for about 3 seconds then
quiets down
- There seems to be some kind of a squeak occasionally when I turn,
brake or start up fast. Not real loud but sharp sound. Just one squeak
and it's over.

Since it started right after the maintenance (not Daimler) it almost
has to be related to something that was done. I've gone to the same
shop for 20 years so I know it's not a rip off, but it almost has to
be something that was done there. It almost sounds like there's some
sort of malfunction with the filter that there isn't enough pressure
unless the engine revs are up.

I dunno what is going on, but it's the darndest thing I've ever come
across.

Any help would be greatly appreciated.

Hank