I have the 99 Dodge in the signature. So you can know the full story, here goes:

I started modifying my truck with the Hughes Engine aluminum plenium and a 180 degree thermostat. Then came a programmer. Next was eliminating the death wobble. So I bought a BD Diesel adjustable track bar kit, but the clearance wasn't enough. I would bottom out in potholes, beating my new track bar bracket senseless. So I bought a 2" leveling kit that bought me the clearance I needed. Then my rear axle died, so I had it rebuilt. Then my front axle died, so I rebuilt it myself. At this point, I installed cheap shocks, thinking them adequate. Then I scored a set of 37" Military surplus rims and tires. Being a man of biggest tire with least lift, a little trimming of the inner fender wells provided clearance. My decision was that with the axles being newly rebuilt, I would put 5 lug to 8 lug adapters on them until my axles die, at which point I would upgrade. But the ride is very bumpy. I sometimes believe my truck imagines the bumps and responds. These rims and tires are VERY heavy, weighing in at around 140 lbs. each. I was told by some that if my truck was heavier, I would fare better. But, I believe that no problem is insurmountable. What do you think?

 

BTW, I had these tires and rims balanced by a big rig shop. (Ugh, some tires have obscene weights on them.)

 

You probably have D40 Axles. Chances are that they are straining but I don't see why that would make for a bumpy ride. Are the axles regeared? I'm thinking along the lines of the engine or axles straining causing jumping of the tires. My dads truck does it sometimes.

 

Dana 44 front, Corporate 9 1/4 rear, re geared to 4.10. Just regular 1/2 ton axles, nothing special yet. And the jounce is at highway speeds. Also, when my NV3500 croaked, I replaced it with an NV4500. The ride is just really, really rough. Normally not that big a deal, but on a concrete pour day when my back hurts, it's ridiculous.

 

Also, for the record, the 4.10 gears basically removed the NV4500's granny first gear and gave me an incredible overdrive in these 37" tires, if that helps. At 65 mph, I pull around 1850 rpm's...

 

How are your wheel bearings?

 

How much psi in these tires? These are a rough tire to start with, let alone with too much psi in them.

 

Those tires and wheels are a nightmare to balance. Chances are the big rig shop didn't get it right.

 

As said above, what psi are you running in the tires ?. Over inflated tires will give you a very hard ride. When I got new tires on my 08 ram last year the tire shop had them all at 45 psi and the ride was rock hard. I dropped it down to 40 psi and that made a huge difference.

 

I agree with snowbound. Lots of weights are a sign of a badly balanced tire. I'd start there. Can you get the shop to rebalance them? Or take it to another shop?

One other thought: You sure you've got the adapters torqued down right? That could also give you fits.