first thing, pulling over 4000lbs and go uphill it starts to warm up fast, water pump is good, thermostat is new, and no changes, i was pulling about 13k lbs the other day, a short distance but i had one big hill and it got just a coupld markes from the red, i know this cant be normal.
   Starting cold is easy, the glow plug light comes on, and she starts when it goes off, but when warm the light never comes on, but ihave to manually switch them on {previous owner put this switch in} and then sometimes it starts right away and somethings it just cranks, but a few tries and it will come on.  
  Im new ot the turbo diesels so all info is appreciated, also do these engines respond well to chips like i hear the duramax and powerstroke engines do, thanks!!!  1993 3/4ton 6.5 liter turbodiesel  

Hey reclipse. Unfortunately, there are not as many aftermarket mods available for the GM 6.5s as they Duramax, Cummins or Power Stroke.

In terms of your cooling issues, even though the water pump or thermostat are in good shape, if the radiator itself is all clogged up with mineral deposits, that could be your culprit. You might want to replace the radiator itself and see if that does the trick.

With the glow plugs, it seems unusual that you'd have to use them in warm weather. Usually you only have to use them when it's cold.

A good resource for info on the GM 6.2 and 6.5 issues is The Diesel Page. Hope this helps  

Hay man I drive a 1993 K2500 6.5L too. Yes they do have cooling problems Ive delt with them. you water pump may be good but if it is stock output it may not be enough. you need a water pump that puts out 130 gallons per minute. and you need a 180 degree thermostat not the stock 195.You can get a upgraded cooling system from heithdiesel.com or ssdiesel.com they both spcialize with 6.5s. A compsite fan will help too. plus the stock herrison radiator is crap they rot out easy so you could try flushing it but if it is anything like mine its just better to replace is and dont go with one from a regular parts store, I did and it did'nt keep the truck cool when under a laod. I went with the one from SSDIESEL.com it works great. I know it sounds like alot but its worth it once you fix the cooling issues with this engine it will run forever and get great fuel millage doing it. Ive grossed over 21K LB with my truck and trailer no problem. but check out SSDIESEL.COM and HeithDIESEL.COM they have everything and if you are looking for some power a intake, exaust and turbo boost controller will make that engine come alive. hope Ive been some help all my family drives either a dramax or a power stroke and I am the odd ball with the 6.5 and my truck works more and gets better fuel millages than my dads trucks or my uncles.  

i have a 94 crewcab dually, auto trans. since this truck was brand new, cooling under loads has been an issue. in my research, the best mods are converting to 97 and up waterpump (higher volume), fan clutch w/fan (more blades, slightly larger diameter), and the dual thermostat set-up. there are numerous suppliers for these parts. local wrecking yards, ebay, local parts houses. most of the "updated cooling kits" that the websites are selling consist of these parts. do a lil digging and see which is the most cost-efficient way for you. hope this helps