'01 Blazer, 186,000mi, briefly******/shudders going up a hill at 50 mph.

The truck runs perfectly around town. I commute 25 mi to work. When I go on the highway, going up a slight incline or hill, between 50-60, it will intermittently*****/stutter. It's very random. When my car repair guy drives the car it never does it. It may do it 3-4 times during a 30 minute drive to work, then won't do it again for days. The computer was reading misfires, so we checked the wires, cleaned and regapped the spark plugs, changed vacuum hoses, cleaned the fuel filter. Did not go away. He mentioned the torque converter and a transmission overhaul. But I don't want to spend that money if that won't solve the issue. It's not a real performance or safety issue, as far as I know, it just bothers me. And makes me reluctant to go too far out of town. Aside from that, the car runs fine, is paid for, so I don't want to get a new car if I don't have to.