Cuts out when driving at low RPMs

[EArmsF350]

Well a new problem has started in the truck I just acquired. I had a problem earlier with it not wanting to start and stay running on a cold start with cold temps. (30 degrees or below) The new problem is the truck cuts out while driving. It doesnt matter the speed but at a slight load to the moter about 1800 RPM and less, just casual driving not hot rodding. Now when I get into it, it runs good with no cutting out. I have completely serviced the truck with all new fluids except for the transmission and coolant. I just came into the house from the shop from installing new plugs and coil boots, hoping that would have taken care of the issue. The truck has a lot more power but still cuts out. Any suggestions?