1994 grand prix engine

Hey all I have a 1994 grandprix 3.1 auto with a few issues that im having trouble pinpointing the problems, here goes-- number 2 and 4 cylinders have less than 90 psi the rest have 120+ the number 5 looks as though it has a little oil on it from the cylinder. there is a very noticeable putting from the tailpipe and gets worse when put in gear especially reverse.. when you get to at least 45 and youre shifted into in overdrive and the engine is under a load on a flat of uphill the front vibrates but when kicked down to 3rd the vibes stop then when it goes to od again it vibrates again and so forth it doesnt vibrate when the gas isnt pushed.just under a load, i rotated tires and that didnt solve it and it is in good allignment. also changed plugs that didnt help either and a spark test checked good. any ideas would be appreciated thanks.

Might want to have a leakdown test to see where the #2 and #4 are losing compression. 90 when the rest are at 120 seems a little on the low side. The vibrations you are feeling in overdrive could be missfires and when you get the RPM's up are not as noticable. I would start with a leakdown test. The headgasket could have blown between #2 and #4 cylinders.

The headgasket could have blown between #2 and #4 cylinders.

that was exactly my thought.

that was exactly my thought.

Great minds think Alike! :)