I took the blazer out for another test run and I paid closer attention to the shift into second, it shifted smooth but still didnt shift into third. I slowed back down allowing it to downshift back into first and this time instead of creeping into a shift a gave it the gas and at the point where it should have shifted into third it almost felt as if it fell into neutral and the RPM's shot up to around 5k.
Hopefully this info helps...
just an FYI if needed.
i've built automatic trannys for decades. I stilll build them for a living. I build several 700 / 4L60 trannys per week.
I believe your problem is the 3-4 clutch pack. Sounds like your tranny needs a proper rebuild.