Truck idles very high (even after sitting for awhile). Any way to get it down?

While the engiine is idling listen for a hissing sound. i beleive a vacume line may have come loose or broken. Vacuum leaks are the main cause of idle issues

Loss of power, but no mention of rough or inability to idle (including stalling). If those additional symptoms are part of the problem, check for a vacuum leak to the intake. Listen for hissing or sucking noises near air hoses. Look for loose, cracked, or broken air hose connections. Check PCV valve...Cheap to replace, could be sticking, then loosen after truck sitting with engine off. A vacuum leak will not give any light indications, and vehicle will seem to run normal when applying gas, but will want to stall or run rough (or want to stall) when at idle or sometimes when taking foot off gas when slowing down.

This is typical for an engine that has gotten water in the fuel. The best solution is to drain the fuel tank.
SOMETIMES you can get by with using a product called HEAT that is for water in the gas tank during the winter. It encapsulated the water so it doesn't impact the gas's ability to burn - but if the water content is too high, even HEAT can't offset it.

Time for a IAC (idle air control ) motor

check the idlle control valve

Have you cleaned the idle air control valve? If not i would start there.

You may have a bad idle air control valve, I would also check for a vacuum leak, from a vacuum hose or a broken vacuum tee.

idling very fast could be vacuum leak or the temp sensor look 4 a bad vac hose or a leak around the intake manifold gasket as 4 the wipers thy are known 4 that when thy git wet i have tried drying them it worked 4 a little wile till i could re place the wiper control on the wiper motor PS.could try some injection cleaner in the fuel i use it a lot 4 the cars that sit around look 4 concentrated or seafoam at the parts store

replace the IAC or clean it. If it doesnt open when you try to start your engine it will not start, after it cools down it may work and let it start Idle Air Control Valve

Could be either one of these. Or both. Check to see if you hear the fuel pump when you turn the key to ON. If you can't hear anything , the pump is bad . Or going bad if you don't hear it all the time when your key bis in the ON position.