Idle speed and engine temp

[J-Ri]

I just replaced the valve cover gaskets on my 86 Silverado's 350ci engine. Took 3 days to finish it (has time for one on wednesday, busy thursday, other one of friday). I drove it to work and school wednesday and thursday. It was completely normal. After the second gasket on friday, I backed it out of the garage and parked it. Seemed normal then. I went out friday night, and it idled very rough and much slower than normal. If I touched the go pedal at all, less than 50 RPMs worth of throttle, it would smothe out completely. It was running at the normal temp (160 degrees) on my way to my buddy's house, and to pick up a load of firewood. With the back full of big logs (not really much weight, maybe 800 pounds) it would run at 210, with a bit of fluctuation. We started in the city, plently of power, running at 210; then got on the interstate, plenty of power, running at 210; got off on a highway, 55 MPH up and down fairly big hills, plenty of power, running at 210. We got to the bon fire, unloaded the wood, stayed for 4 hours and headed back to town. On the way back it was still running at 210. All I did was the valve cover gaskets, I reconnected all wiring and all vacuum lines. I double checked all the vacuum lines, because my first guess was it's running lean. Any guesses what's wrong? I don't care about the idle, I think it sounds much better like that, but the change in temp (although not over normal) concerns me.