1991 Chevy Lumina hesitates during acceleration

Hello,

My Lumina (3.1L) hesitates or stutters when I try to accelerate, especially between 50-65 mph. It takes off from a stop just fine, and runs well in the regular "drive", but when in overdrive it stutters until I let off on the gas.

Any thoughts? I'd appreciate any help!!

Thanks,
Tom