Have you checked your exhaust? The engine needs to breath well and a plugged Catalyst converter will give the a lot of symptom that are assumed to be vaccum, transmission, or engine problems - not being able to pull a load up hills, shifting poorly and sometimes shifting up and down and making lots of noise at times, poor gas milage and the A/C was shifting to the floor when the engine went under load.
I thought was in the transmission -I took it in for an evaluation at a good shop (Cost me 30 bucks) He check the computer, took it for a ride and when he got out he said nothing wrong with the trans. It's the engine - it's not breathing right and the computer does not know what to tell the trans to do.
Had the cat replaced and no problems now.