Fast idle at normal operating temp

I recently purchased an 84 Suburban with a 350 to haul my boat. When I picked it up the owner said that the carb needed rebuilt so I ran it to the shop and had that done before I really drove it very much. While it definately starts and runs better than before it has some problems once it reaches normal operating temp. The idle increases dramatically at these temps, I can idle at about 35-40 mph, and it has developed a habit of dieseling when shut off. I assume that these are carb problems but I'm no expert so any help would be greatly appreciated

Thanks in advance

I bought my Suburban new in 1986, it's got over 215,000 miles, it's still being driven daily and going strong. It has, at times, idled a little too fast, usually due to adjustments made when it wasn't running its best. Over the years it has had at least one carburetor rebuild, within the last couple of years, but I think there was another sometime in years past. Since you recently had the carburetor rebuilt, I'd bring it back to the shop that rebuilt it. Hopefully, it just needs adjustment.
If you've never had a Chevy truck of this vintage, here's a couple of things to note:
Good ignition wires make a world of difference. Almost every time that my 86 ran really rough, a new set of ignition wires was part of the solution.
Fuel pumps wear out. I'm on at least my third one.
If alternator must be replaced (usually because the diode fails), go ahead and get a new battery, if not simultaneously, then soon thereafter. Conversely, if you battery gets bad, expect to have alternator problems. Each appears to be very dependent upon the health of the other.
That's all the negatives of my 86. I think that's a pretty short list. May your 84 serve you as well as my 86 has served me. Send an email to me so that we can compare notes and resources as we care for these good old horses.