The T-5 swap is a good one but it alone doesn't help your highway speed. The problem is your low geared rear end.
Use the search function of this forum to find threads about rear end swaps. There are bunches of them.

"It's just a phase. He'll grow out of it." Mama, 1964

1956 Chevy 1/2-ton 3100
1953 Chevy 6100 "The Yard dog"
1954 GMC Suburban Now with a new proud owner.