TH350 Shifting Questions

[Hack71]

I just bought a new project, 1971 C10, From what I can tell the driveline is original, maybe? It has a 350 4bbl with a TH350 Automatic. It shifts at the correct time, downshifts good etc. Its been a long time since I've driven a 1971Vintage Truck, 25 Years or so ago. I don't remember letting off the gas and it slowing down almost like a engine brake would do. I had a TH400 that acted more like that, so I'm curious if this might have a shift kit or other mods done to it. It does shift firmer than I remember as well, it has 373 gears, and seems to be running higher rpms @ 65 mph I haven't installed a tach yet to see what the rpm is. I will be using this truck for cruising around and want it to be street able, I'm not looking to win any races and might even want to travel with it. Might consider a gear ratio swap, or a different transmission to be able to cruise at 70 mph for long distances Any Ideas, Thanks