hi, have a 2001 DRV 3500 that vibrates/shimmeys slightly between 40 to 45.
Tire balance and alignment check good. This only happens when accelerating on flat or uphill grade. No vib. down hill on acceleration. Also if I back off gas (coast) between 40 and 45 no vibration (as in not tires). Replaced idler arms and lower ball joints with Moog parts a year ago with at least 5,000 mi. since with no vibration.
Any ideas would be greatly appreciated.
thanks

Yes about 7,000 mi. ago. I will check for play there though. I have recently been parking on a moderate grade and van would lurch a little from park to drive or reverse. After about 30 starts that way I now set the parking brake.
i forgot to mention in original post that one of my upper ball joints started "creeking" just a little bit so lubed both sides and noise stopped.
Thanks for your response

the vibration is slight and felt in the body (thru the seat) not the steering wheel. It feels exactly like out of balance front tire(s). Besides having balance rechecked good on fairly new (5,000 mi.) quality tires if I take my foot off the gas the vibe goes away instantly. Coasting at any speed will not cause vibe. The engine only has 86,000 mi. and runs smooth as could be. Tranny shifts smooth also.

You Tube

That app is cool but at $399 I'll never try it. I think it's narrowed down to shaft, ujoints or pinion angle. When I do find out I'll post back. I thought this problem just started recently but realized the last month is the first driving I've done outside of very flat S. Florida so might be first time it would show up.
Thanks very much for everyone's help.

Thanks, I will start there.