I recently picked up a 95 suburban. Tbi 454/ 4l80e.

Nice truck. I've been working on catching up some maintenance and a few things the PO had let go. I have it in pretty good shape except for the idle. It idles 1000rpm out of gear. 800-900 in gear. Even when fully warmed up (hours of driving)

i did did all the normal things... Checked for vacuum leaks, changed the tbi gasket, cleaned the iac, etc. nothing has changed it. The only idea I have left is the PO did brag about having a 180* tstat in it "so it would run cooler" which it does this time of year. Seems to run right at 180. Don't know if the extra 15* of the factory tstat would make it idle down?