My 95 3500 Cummins is used to tow. Total rig 19,000-20,000 lbs. It has a #10 plate, Timing advanced to 15, 4" exhaust, 3000 governor springs, boost upped to 30psi, NV4500, aftermarket 13" clutch. So it needs a head gasket and trans refresh. I'm sure the injectors could use a look. What to do? clean or upgrade. Wastegate is seized so I should get that as well. Whose head gasket?
Doug

Spend the least amount to keep it running strong and reliable. I've seen the Victor Reinz gaskets used for Cummins rebuilds. I would see what the modified-stock truck pulling guys are using for gaskets, wastegates, trans stuff, etc.. just for curiosity.

Keep the tow rig strong and reliable so you can be sure to get your awesome Belvidere to the races. Spend any saved cash on racing!
Mitch

With the weight you are towing I'd keep the power where it's at. You will run into EGT issues with anymore fueling than you have now. NV4500s are weak in several areas. The stock 1 1/4 input shaft can break with a with extra power and a stout clutch. If you are going to a 13" disc, I'd upgrade to a 1 3/8 input shaft as well. 3rd gear and 5th gear are also common problem areas as well. Later style head gaskets have thicker fire rings and are better.

Clutch has been in it for 75,000 miles. It did have the 5th gear nut come loose while under warrantee in 96. I always use 1st gear when starting out with the trailer. It actually pulls pretty well. Just thinking that the injectors should be at least sonic cleaned and checked. That's why I was thinking if I were to upgrade the time would be now. I've never seen the EGT above 1200 even up long hills.
Doug