have you checked the ECM for trouble codes?

sound like you are having multi problems with the engine.
my wife has a 86 firebird transam, the original 305 in it bit the dust 4 years ago,

I had a problem with my electrical and ECM for far to long and I had to remove all and rewire the whole car. I dont think is your problem I just wanted to share that with you.

did all of the lifters build back up?
if it were me and I had them out to clean them I would have replaced them.

when you removed the intake and other parts to get to the lifters did you take pictures of the vacuume hoses and where they go, as to make sure they went back where they should be?

when installing the new intake gasket did you make sure it didnt move out of place, did you torque the bolts in an alternating sequence like it shows in a shop manual?
and did you torque them in stages of 3 to prevent warping the intake?

the reason im asking is you could have a vacuume leak from a hose or the intake itself.

if you have more oil coming from one pushrod than the others , did you clean all pushrods and I would have checked them for bent.

if you pulled the lifters and reinstalled them could you have gotten them mixed up?
they should go back in exact where they came from, or you will have problems.

hope you get it fixed.