Hesitation problem 292ci

[todds66]

Hello all, I need some help trying to figure this issue out.

I have a 1968 C-10 with a 292 (yes it is - special ordered) in-line six with a four speed manual (stock). The truck runs really well around town and below speeds of 50-55 mph. However, when on the freeway doing speeds 55 mpg or so the truck seems to stall, lack fuel. If I let off the accelerator and let the speeds go down, then slowly accelerate, it again it takes off fine up until I get to that same 50-55 mph speed. The engine consistently does this almost like there is some type of governor restricting freeway speeds.