1990 GMC K1500 No Uphill Power Part 2

[LynnJr]

Truck is a 1990 5 speed 4x4 1/2 ton 350 TBI with 20,000 on a gm crate motor.
No catalytic converter and most everything on the engine replaced atleast once or more.
It had a 165 thermostat in it and no error codes even though the spark knock sensor wasn't hooked up.It was replaced.
I put a 192 degree thermostat in it but never had a chance to drive the truck until today.
On the highway at 70 mph I shifted into 5th gear and the truck felt rough then popped through the throttle body and threw error code 43.
The temperature guage inside the cab is also bouncing all over the place now.It will read 210 then bounce to 165 then back to 210 then to some other number.
I drove it for about an hour and it seems to run okay when running it through the gears hard but after a gear change and lower rpm it seems to run rough then it cleans up.
I am going on a 14 hour trip saturday and am willing to shotgun a bunch of parts if necessary.
Give me a list.
Lynn