Sorry, y'all for the slow reply. I went on a trip for my 1 year wedding anniversary with my wife to Savannah, GA and we left our electronic devices with access to the internet at home... fun trip.

Anyway, I can't say how "new" the problem is. I never drove the truck in this kind of temperature until this year when my '86 Daytona bit the bullet (going to try to rebuild her but it will be a bit) and I didn't have a great paying job up until last week so a newer car should be in order very soon. In short, I may have had this problem since I bought the truck several years ago and just never knew it. It has been in the mid to high 90s here with heat indexes over a hundred and the air coming up off the interstate is probably pushing boiling.

The details on the build are going to get messy so hold on (but not as modified as Feets):

1968 D100. Engine was recently rebuilt (though not original) and has less than 3500 miles (but is close to 3500 miles). It is a 440, 0.040 over and the pistons are .100 in the hole (reuse - no budget - don't poke fun), with stock rods and a forged crank. Heads are Eddys (purchased a few years ago) that have been milled for a final compression ration of 9.2:1. Cam is a Lunati 60303 with Lunati lifters and Trend custom pushrods because I'm running Harland Sharp rockers (and that's where the budget went). The oil pump was rebuilt to stock specs and I get great oil pressure even without an oil limiter to the heads. I am running full length headers and 2.5" dual exhaust. The torque converter is from Turbo Action. I run a small oil cooler in addition to a deep trans pan. The fan is a 7 blade from a '76 or so Chrysler C-body of some kind. The water pump and t-stat are new Milodon units. The water pump housing is a factory Mopar unit. The fan clutch is a new thermostatic heavy duty unit made by Hayden. It get very stiff when the engine is hot. The fan moves a lot of very hot air. The rad cap is a newer 15-16lb unit that could be found on any Mopar from the 80s and 90s. The carb is the cheapo Holley 750 (74 jets in the front and a plate equal to 75 jets in the secondaries). I run 18* initial timing and 32* total. I have a Mopar Performance dizzy that I've set up based on advice from here. The total timing doesn't come in until 3500 rpm and the vacuum advance has been pulled back quite a bit. Plugs look great (Champion RC12YC).

The radiator itself has been recored. It is from a '68 C-body that had a 440 and AC (according the the part number). Unfortunately, the radiator and engine are not in the same exact orientation in the truck as they were in the car (the rad sits an inch or two higher) and the the fan is a few inches bigger in diameter than what was used in the original application. While I do have a correct fan shroud (in perfect freaking condition), I cannot use it. I ran without a shroud for a long time but when the air temps got over 85 or so I had to add the shroud. I hacked up a shroud from an '80s Dippy. It actually fits very well. I've sealed around the top and bottom with double sticky sided foam tape and the sides are more well sealed than they were in the Dippy.

Because the radiator was a recore (though via a reputable local shop) I am a little worried it wasn't done well and isn't flowing water evenly. I do not have one of those fancy laser guided temp deals so I guess I need to invest in one.

The temp gauge is the stock factory gauge. When things are humming along nicely in cooler weather the gauge points straight up (between the letters "E" and "M" in the word "TEMP). But now that it is warmer moves to the right (past P) and I get nervous. Once again, I guess I need to confirm how hot it is getting but it does want to start pushing out coolant when it gets real hot. I have no puke tank.

Thanks for all the help guys. I guess I have some things to look at.