It has approx 90K miles, no check engine light. It is very sporadic, it almost feels like it is running out of gas or loading up on fuel, but no black smoke as far as I can tell. If it is a weak fuel pump, would the OBII monitor that?

I also read about a 2.5 having somewhat similar issues but his check engine light came on and he found the cause to be a leaking fuel cap seal.

Would it have codes if the fuel pump were starting to go out?

altimas have probs with oil getting into distributor--an oil leaks from around the distributor area?

Also get some MAF sensor cleaner and give it a spray.
My 95 eats distrib. cap and rotors--check those also