Trans. allways shifting???

[Prop_Washer2]

Well the old 350 probably had a little more torque and maybe at a little lower rpm. Also the two may have different gear rations, i.e. 3.73's, 3.55's etc...could be different between the two. I had a 1996 Dodge Ram 4x4 extended, and it had a little 318 (5.2 Litre) and 3.55 gears, it would come out of TC lock up, on any slight incline at 60 mph...pain in the butt.
You might be able to check your Gear Ration by using the VIN number, one digit there represents the axle ratio...someone else on the board here may know...