TH350 feels mushy, havent driven in 5 years

[George]

Got the enging running after 5 years. After I remembered there was a hidden kill switch under the dash...... It started right up and seems to be running strong.

The trans feels mushy, I do not know the stall speed but it doesnt engage till Im probably 2k and higher and then it just speeds up slowly. When I punch it, there is no immediate response it just speeds up a little faster, but the engine revs nice and strong.

The fluid is full, and was supposed to be newly rebuilt when I bought it 8 years ago. Ive never driven it much, but before it felt more solid except I never had the engine running very well (never properly timed it till now). It is clean with fressh seals and looks to be a new rebuild unless they cleaned the hell out of it to make it look that way.

Anyway, I may change the fluid and filter and see if it does anything. Do I need to just drive it a little and get the fluid flowing again?

I may be eventually swapping in a 2004r since my motor is fairly mild so I dont want to dump money into this trans but I would like to get it driving as is if possible.

Let me know your thoughts on how to handle a TH350 thats been sitting for 5+ years. Thanks in advance.