4L60-E sluggish shift

Hi all, 02 Blazer 4X4 4.3L 60,000 miles. Transmission shifts fine coming off the line from a dead stop, but when I'm on the highway and I give it a little gas to get over a hill the engine noise increases but the truck doesn't seem to accelerate right away. I have to push the accelerator far enough down to engage the passing gear just to maintain my speed on an incline.
Trans fluid and filter change at 35,000 miles,looked clean, no malfunction indicator light lit on dash. Terrible gas mileage.(14 mpg).
Did full tuneup in the last year; plugs, cap/rotor, fuel filter, air filter. Did rear brakes, rotors pads and e-brake shoes last week. Caliper pin was stuck, lubed it, checked all wheels for brake drag, but this hasn't fixed the shifting problem.
Is there anything obvious that I should check before I bring it to a tranny shop? I've heard there are adjustments they can make such as tightening the bands. Would this help?
Also is there any way the tranny shop can program the PCM to provide a firmer shift? Thanks