I am borderline panicked.. My 4L60-E in my 94 Blazer Tahoe LT seems to not want to get out of 3rd.. Revs very high for 60 or 70MPH, with a LOT OF power. Like it is red lining in 3rd. Though selector is in Overdrive.. my fluid level is perfect.

What happened???

 

Sounds like you're 3-4
3/4 BONDED STEEL CLUTCH PISTON, Is not closing.

Brand New 3 4 Bonded Steel Clutch Piston 4L60 4L60E 4L65E 4L70E TH700R4 700 | eBay

 

Can you quantify the changes in revs? Was it 2,500 RPM's at 60mph before the change and 3,500 RPM's after the change? or was it 2,500 RPM's before, and now it's 5,500 RPM's?

Are there any trouble codes in the ECM? You can read them by shorting two pins on the ALDL (like with a paper clip).

Here's a how to: https://www.obd-codes.com/faq/read-g...codes-free.php

If the change in revs was ~2,500->~3,500, it's likely related to the 3-4 clutch. It could be the piston mentioned by Boondocker. It could also be the shift solenoid which controls fluid flow to that piston, or the 3-4 clutch itself.