I have a 66 c-10, the motor gets hot at slow speeds. Do I need an electric fan or find a shroud and clutch fan??

What radiator are you using? The one that was with the original engine? If so I recommend you get a heavy duty radiator, keep looking for a proper shroud and look for a chemical additive that disburses the heat from the coolent. Sorry I don't remember the name.

Do you have a lot of chrome on the engine? Chrome parts retain the heat. Also did you build up the engine for more HP? The more horses, the more heat produced. Find a four row aluminum radiator, run a 160 thermostat, and you might consider putting louvers in the hood to vent the heat out of the engine compartment. You have the heart of a Clydesdale horse in a Shetland pony. If you get the bigger radiator, find a good electric fan that will fit into your configuration. I took the thermostat out of the fan wiring loop and have the fans run full time. It helped in my engine build up in my Corvette. Taking the fan off the pulley system will work it less and give at least a ten HP boost. Replace some of the chrome with polished aluminum also. This will help remove the engine heat.

Still can't find a shroud. Would an electric fan work best or a clutch fan

The correct clutch fan is good bit if you can get a good electric fan you'll add a few extra horses.

I'm going to state the obvious here; A stuck-open or missing thermostat will cause this problem. Symptoms are 1. slow to warm up. 2. temperature gauge never settles down to a consistent reading and varies with engine RPM and vehicle speed. 3. Coolant flows through the radiator immediately on cold engine start. If you bought this truck in the deep south, many backyard mechanics will remove the thermostat thinking they are doing their engine a favor and wonder why they overheat while sitting in Houston traffic in August. Obvious, yes, but often overlooked!