'79 450SLC - loss of power

I have a 1979 450 SLC that sat for an extended period of time (1-1/2 yrs) before being driven again. It has been driven for short periods of time since. On my last drive, I took the car out to keep the battery up, etc. It was running fine, though a little hot. High oil pressure. Fairly smooth idle. I ran it at low and high speeds on the highway. After about 45 minutes, while cruising at about 45 mph, car starts to buck a little and lose power. Felt like it was running out of gas. Gas sender needs to be changed so reading is inaccurate. After fill up, I confirmed it still had plenty of gas when bucking. I left the car idling while filling up. While at the pump, it eventually stalled while running rougher and rougher. Was able to start again easily, but still running rough and with loss of power. Got the car home, barely. Kept stalling while trying to park. At home, I could smell something akin to what you would expect when doing plastic injection molding or one of those kid's hot plastic former games. It seemed to be from somewhere mid to back of car.

Any thoughts??? Thanks. SMW