OK the speedometer does not work so I'm guess at the speed..Yet there is a rumble noise that starts at some speed around 35 then once you get Up and running rather quick enough..It settles down to be rather quite....
Any thoughts??
It's a b2500 ram van 1997-- 5.2--318...I just finished with redoing the whole front end new moog control arms end links wheel bearings ..shocks...
Now I'm doing the drive shaft universal joints. and rear shocks..

I just might be the tires, hell it could be lots of things...I'm putting in a new upgraded spring in the trans..too..tomorrow....
yes tomorrow its rear shocks and universal joints and that compressor spring...

tonight I just watched the new star wars movie...we like it...

 

Really hard to say without more information. Rumble sounds like tires to me. Alignment may be off. If it wasn't a thing before the work, odds are its the result of the work.

 

post a pic of the tires.

 

I wonder if you give it a little more pedal to get up to speed quicker, do you still feel or notice that rumble? I'm no expert but at 35-40mph and light acceleration the transmission has shifted to o/d and strains a bit harder to until speed is gained.
See how it does after replacing the u joints. Just a thought here, it wouldn't hurt to check the transmission mount and motor mounts for excessive wear and play.

In 2012-2013 or so my van's rear end took a dump and the van sat in my driveway for 2 years. finally found a guy in town that could rebuild it(others wouldn't touch it) and get it on the road again. He test drove it with me and noticed a vibration and slight thumping while driving it around town and told me the tires were pretty well worn and probably had developed flat spots causing the vibration and noise, sure enough that was it and new tires cured that problem.

 

thanks Jfloors-- I just pulled off the rear tires, and lifted the rear end,,,blocked the front tires,and put it in drive...What a racket!! I took a quick look to find the hubs loose, So I pulled off the hubs...re'tried..In drive....slowly raised the speed..and found the heavy vibes in one area of speed..
sense I can't depend on the speedometer...It starts at about 35-55..its pronounced....

So I put it all back together...It is now most likely 'the drive shaft is unbalanced'....or even rear axles...

So now I will pull the driveshaft off again..and drive it the 50 miles to the driveline service shop....I'll call them on monday..see what they say..
again thanks Jfloors...