86 s10 blazer, looses power at 45-50 mph

I have an 86 s10 blazer. 2.8 v6. It starts and runs fine cold at low speed. At 45-50 mph it won’t go any faster and will stall when I stop. Will restart in 5-10 minutes, but runs ruff. Here’s the kicker. When stopping after trouble starts, braking becomes very hard, obviously loosing vacuum. Replaced 02 sensor and control module and all standard tune up parts.

Restricted exhaust is a likely cause.