When I am driving on the highway and step on the gas the RPMs go up but no pick up, shift is hard and I can hear what sounds like a vacuum leak when I am driving by the retaining wall on the highway. Can't find a vacuum diagram for the entire engine and trans. Shifts fine when driving like a granny. But if you want to pass you need 100 yards to get up to speed.
The trans fluid is red and full.
97 blazer S10 4.3 4x4

 

I was having the same exact issue with my 2002 4.3 BlaZeR2. I took it to a local mechanic who did a smoke test to detect vacuum leaks and found a leak in my lower intake manifold gasket.