Got the car running OK with this new PROM, but it seems to fall apart at anything over 75-80% throttle. Hard to explain but it sputter's and pops. Sounds like misfiring. Just wondering what in the PROM can I change to try to fix it? Car idles and drives fine now, this is the only problem. Could it be a PE timing problem? Too much or not enough maybe?

Try both. I had detonation the same way and it ended up being my eprom was telling 0 base when in reality my car was at 8. That accounted for detonation that was unrecoverable.
Zero out your PE table and see if that cures the problem, then do all the math and figure out your actual timing. I'm not sure but doesn't the 165 scanning software spit out advance in the aldl stream?
I'm currently only running max of 3 degrees of PE timing which I need to modify. The car runs GREAT even with zero degrees in the table. Enough that I can be driving on a 90+ degree day and rolling 30+mph, punch it to the floor and spin the tires on the downshift (and it's an auto ).
If you figure it out please post a reply.

I am having the same problem...

I'll try that and let you know how it goes.

If it seems to pop out the intake then it's very lean. Add some fuel in the PE table for safety, then take a test drive.

If that helps it out then go back and re-tune the part throttle...

The VE tables are fine. Under normal acceleration and part throttle it's fine. It's only under 75-80% throttle (when it seems to go into PE) that it falls apart. What would happen if I didn't let it go into PE until a higher throttle percentage? If I do this and then notice that it doesn't sputter until a different throttle position then that would narrow it down to a PE fuel or timing problem, correct?

In a perfect world yes but nope. Look at your MAP and you'll notice that the main spark table at 80-100kpa will only be touched when you open the throttle fast and/or near WOT. So your main spark table and vol eff tables could also be hurting you. This is why I (Grumpy's tip) like to zero out the tables for PE and other misc so as not to confuse the situation. Many a times I've been chasing my own tail only to find a stock calibration table to be far from effective. The GM ecm has a lot of tables in it, get into source code and you can break things down into useful code and useless tree hugger code. Maybe even add your own like the ignition retard vs vehicle speed . Or expand your main tables to have greater resolution.

I can't look at my MAP values. It's a MAF car . Can you tell me more about this source code stuff? I'm definitely not a big fan of the tree hugger modes at all