95 Jimmy Stumbles on Acceleration

It is a 95 Jimmy with the 4.3L Vortec. It has 160,000 miles. When the engine is cold the problem is not there, as soon as the engine gets a little warm it sputters and stumbles on acceleration. I removed the upper intake to check the fuel regulator and spider. The passenger side of the intake is fairly clean, but the passenger side is black and has standing engine oil in it, (When I spoted fluid in the intake I assumed it was fuel from the fuel lines but it feels and smells like oil). I still think the fuel regulator or leaking fuel lines are the culprit but there is no fuel in the intake and I can not see them leak anywhere. Any ideas on what is going on? Thanks for your help.

Run a fuel pressure test and check for fast leak down.
If upper intake is off hook fuel lines back up and jumper fuel pump and look for fuel leaks and fast leak down.

Post back fuel pressure reading.

Does it stumble at idle or just upon acceleration?

Does it stumble at idle or just upon acceleration? It only happens under acceleration. If I lightly apply throtle then it is not as noticable, If I mat it then it stumbles worse.

Run a fuel pressure test and check for fast leak down.
If upper intake is off hook fuel lines back up and jumper fuel pump and look for fuel leaks and fast leak down.

Post back fuel pressure reading. Does the oil consern you or is that supposed to be there, it seems weird to me, I have never had an intake manifold with oil inside.