Jim,
Well I cant match all of what happened but here is what the Gonkulator says (all with 3000 stall)
Powerglide 3000 stall
2.22
10.02 at 68.5
15.77 at 85.0
Powerglide 4000 stall
2.31
10.04 at 68.7
15.78 at 85.1
T350
2.02
9.68 at 69.4
15.42 at 84.8
200-4r
1.99
9.67 at 69.1
15.43 at 84.6
Unless maybe those 69mph you gave are 1/8 mile mph, I cant get anywhere near them, not sure what is going on there. Maybe you are on the brakes at the traps or something? Hi-15s and 69mph does not seem to go together!
In any case your setup seems right on as it is, I was surprised the 4000 stall showed no gain and even adding a gear only gained a few tenths (often it is way more than that). For me I'd leave it alone, or add the 200-4r if it's a freeway cruiser. The T350 to me would not be worth the swap.
