With EFI you don't want to run a 160 t-stat without a PROM change. The truck may run fine, but will be running too rich all the time, because the ECU will still be feeding it warm up enrichment trying to see a temp of 185 or better. The lowest t-stat you can run is a 180 without problems. Given the cost of gas do you really want to be too rich?
I agree with the consensus here. A lower t-stat is just a crutch. Fix what's really wrong. Another thought is the condition of the radiator. If it's clogged up with mud it won't radiate heat as effectively. A good pressure wash session at the local car wash can aleviate this problem. I've seen a lot of rigs run hot from this condition.