Apologies for the delay in my reply, for some reason the alerts for new posts didn't come to my email anymore and as I logged in to the thread tonight I see there were a few more since I last looked.
Anyway, I finally got the van back from my buddy's shop. I had him do quite a bit, and he says I owe him for chiropractic bills since that big sliminess bumper made everything a bit more difficult than it had to be! Here's what we did:
1. replaced the OEM radiator with a performance radiator all-aluminum version. I thought this was "preventative maintenance" until we got it out and did find that there was some hairline cracking on those plastic crimped-on end tanks so I'm glad we did!
2. Since we had the radiator out we also replaced the fan clutch with a new OEM one.
3. Also put in a nice 10" electric fan (with a toggle switch in the cab) in front of the radiator and transmission cooler. I wanted to put in a bigger transmission cooler but we couldn't find a way to get a bigger one in there without doing some serious surgery to the front end, so I am hoping that the electric fan helps both coolant and transmission temps. I like that billet grill less and less every time we're in that engine bay... but I'd like to find something better than the OEM one to go back to too. The fan is very quiet actually, you absolutely can't hear it over the sound of the diesel engine.
4. Also replaced the thermostat with the low-temp matsumoto (thank you Twoxentrix!)
5. Got a tune from 5-star to kick the fan on at lower temps but have not yet loaded the tune. I'm curious to try this out so I can a) hear if the fan is any quieter and b) if it makes a difference with temps
As far as the results... well, that will have to wait probably, it's hard to tell now that it's "winter". It was 110 in Phoenix and I was towing when I was reaching those higher (~240F at grade) temps. Now it's like 70 for the high, and we got rid of our trailer. I will certainly post results next summer, but to me all of this stuff can only help so why not just get it all done? At this point with almost 200k miles on it, and only 10k of those miles mine, I am going to assume that if I haven't replaced it, it's got 200k miles on it and replacing it can't be a bad idea.
In the meantime while weather is nice I'm on to making some changes to the interior (separate threads so I won't sidetrack this one) - putting in an L-Track system for seating, getting a CCV pop-top, shore power, solar, etc. I'm finally starting to understand all the jokes on this forum about not ever adding up your receipts!
Thanks all for your help! Love this forum