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?