I was racing yesterday and when I punched it at about 80 miles an hour it felt like my back in was shaking very violently and more so on the right side.  What can be the cause of this problem.  Could it be a  loose tire or is my rearend going out?  I immediately stopped and went home after that but was just curious, is this something that I need to upgrade the whole rearend and if so, whats a good site to go too?  My lift is a Fabtech and I also have the chrome and black DC1 wheels from Dick Cepek.  Any information will help greatly, thanks.  

First thing to do is check all of your u-joints. One may have fractured or seized. Check the drive shaft(s) also for any signs of twisting or cracks in the welds where the yolks are welded on. Also check for excessive play at the slip splines and look at the carrier bearing if you have one.

If everything looks good there, pull the axles shafts out of the rear end. One may have broke. It's easy to do, you don't even have to jack up the truck or take the tires off. Just remove your hub cap if you have one. There will be eight bolts on the face of the hub. Remove those, grab the flange the bolts were holding and pull the entire axle shaft out. You may have to pry a little as they are sealed with a gasket or silicone. The end of the shafts should have a splined section that mates with the differential. Check these splines for damage. If everything looks good, the axles will simply slide back into place. Put a thin coating of RTV silicone on the flange to keep the gear oil from seeping out and throw the bolts back in.  If an axle comes out without splines, it has broken and you will have to pull the diff cover to fish it out.

The rear ends in these trucks are extreamly strong and there are many guys pushing well over 1000hp through the stock rears without issue.  

you may also check you fluid levels, if you have a blown seal internally and its filling the axle tube with the gear oil, you could have ran the thing dry and damaged your spider gears or even a bearing, it does happen, even on stock trucks.  

what year and model is your truck  

It's a 2007 Dodge Cummins 5.9.  The thing is though it doesn't do it all the time.  Only at highway speeds will it do it, but it won't do it all the time.  It's a bit hairy, and a bit scary, but if anything I will have to upgrade it or something.  How often do you have to fill the fluids, it's got 22000miles on it.  One guy told me it could be my converter, it's a BD Converter so how reliable are those, I heard they were good to 1400ft lbs, could it be possibly that my converter could have been faulty and if so could this be linked to my shuddering?  

as new as your truck is, id say something is wrong with your rear end, its gotta be a bearing somewhere.  fluid intervals are 60-75k for your truck.  I highly doubt itd be your converter, itd do it at a certain RPM in all gears if it were.  

How can I check the bearings then it it?  

jack up the rear wheels, put chocks or bloacks in front of the front wheels and put the tranny in neutral, then spin each back tire and feel for any binding, also listen for metal grinding noises, also try gently pulling up of the tire, if it moves without the whole rearend going up, then youve got a bad bearing and possibly a broken axle.  

ok then, I will check it today and follow up with you. thanks....  

UPDATE!!!!!!!!!!!   It's most definitely not the driveline.  I took it to a mechanic and he said that when it shuddered like it did, it wasn't the driveline at all but it was the motor.  When it shuddered it shot out WHITE SMOKE and he said it is a fuel related problem.  Could it be the injectors?  I heard that the Diablo Sports are hard on injectors and so is the low sulphur fuel, also could it be my CP3 pump?