I would change the oil, run it hard (but not so hard the rods exit the block!) for a few hundred miles, change the oil again. Do this several times. If this does not help then I doubt anything short of a teardown will. My opinion.
I have already gone through almost 30 gallons of gas. I can't believe how well it runs. I'd have never guessed it would have this problem. I have a T5 MT with the 0.73 OD gear and a 3.73 rear with 29" tires and hills are no problem even if the RPMs get down around 1700, I can still accelerate and pick up speed easily. Seems to have plenty of "pep".
I'm using 5W30 oil right now. Is that making things worse? Adding to what Stroker6 said. Use rotella 15w40 diesel oil. It is a high detergent and will also help dissolve carbon deposits.
Alternatively, using a quart of ATF also adds tons of detergent. Drive it lightly for a week and it will clean out.
Should I just add ATF to the oil and skip the kerosene wash out?
Any comment on which block to build if it comes to that?
