2005 Chevy blazer SUV
155,000kms
4.3l Automatic v6 4x4

I've used the search engine but never really found anything specific to my issue. Maybe I can get some insight from you guys.

Took the blazer in for some transmission work done. Turned out the coolant contamination called for a huge job. New torque converter (as it was shuddering from having coolant in it), seal kit, overhaul, everything. All done by a certified automatic trans technician. My problem is its been almost a month after its repair and I've been noticing a loss of power going uphill (normally I can give it some extra gas and i get a nice kick up the hill. not so much now). Its not a terrible loss of power but its noticeable. When I go from a stop and start to drive uphill it feels quite sluggish, compared to already being up to speed. The other day I experienced a check engine flashing while going uphill on the highway. Once I reached the top and let off the gas the check engine light flash went completely off and never stayed solid.

When I got home I plugged my obdii diagnostics in to pull any codes, but there were none. Just a flashing Catalyst monitor with a question mark for a pending code. I drove the vehicle for a few days and hadn't noticed any further loss in performance. So once again I plugged my diagnostics in, and now I get the green check light and no flashing Cat monitor. Was this just a random misfire from bad gas? Should I have gotten a tune up after getting the transmission work done to bring her back up to health? Or is there a potential issue with my new torque converter?

All in all I feel the transmission shifts well. Sometimes if im heavy on the gas it revs up to 2.5/3 before it shifts. No free revs or grinding.

 

I assume you have fixed your problem by now, but as I had the same issue and could not find the proper answer on this forum, let me post it here:
while many point towards the fuel pump or the MAF (which can have similar symptoms), in my case the problem was air loss at the upper intake manifold.
When you revved the engine from the engine compartment, it sounded like a hole in the exhaust system at first.
It became so bad that in the end I could only go 10-20 mph if there was the slightest incline, because as soon as I gave more that 1/3 gas all the air came out of the leak instead of going into the engine, and the MAF threw an error code.