It's probably junk in the TCC, I've heard this RPM fluctuation thing is fairly common. They have some shudder fix stuff you can pour in as a temp fix, generally the long term solution is a new Torque convertor

 

Sounds like you made a lot of progress on getting your transmission to functioning better.

It is good that your TC is locking up correctly at 60 MPH and is unlocking when you touch the brakes. If it keeps locking/unlocking at 55 just keep it out of OD if you can not drive 60+ MPH. Over time the making/breaking TC lock up may get better with use. If you drove it much in second the ATF may have got hot and foaming is a change out of ATF would be in order.

Keep us updated concerning the outcome.

 

i changed the atf out when i redid the shift solenoids about 2-3 weeks ago. haven't drove it since i test drove it then too.

i did some researching and came across and old thread

https://blazerforum.com/forum/2nd-ge...on-surge-2832/

unfortunately he dumped alot of money into it and never found the cause and it sounds pretty close to what i have.

although mine seems to run pretty good. slight miss at idle but it has probably about 8-12 month old gas in it and needs new fuel..

i might try replacing the MAF.

i do run a k&n cai setup and i cleaned the MAF awhile back just as preventive maintenance but that doesn't mean it couldn't be bad.

i'll probably pick one up at the junkyard this weekend sometime. what year MAF will work? 98-04 or can i go earlier.