quick background:

i dumped 20W-50 dino oil last week and added 2 gallons of 10W-40 dino, new filter and also 1.5 bottles (~18 ounces) of auto-rx additive. then i went away for a business trip for 5 days.

when i came back and took her out for a 'ride', i immediately noticed that the engine would only rev to 5000, and also it would rev slower??? i recall the car pulling like a freight train but it doesn't pull as hard especially above 4000rpm.

i then checked the oil level when i got home, and it was past the max.. i ended up draining almost 1 full quart of oil to get it below the max level. wtf

any ideas?? could the excess oil cause sluggish engine performance?

Excess oil can cause all sorts of problems. I'm pretty sure that you have hydraulic lifters in that engine, which won't like foam instead of oil. Neither will the bearings or camshaft lobes.

Two gallons plus 18oz is too much oil, but you know that already. Hopefully you didn't do any permanent damage.