thats what i was getting at. total weight is prob between 12 and 13 K. ...... maybe your next upgrade should be a nice 12 valve cummins

 

I wish I could go back and redo my purchase. I was looking at cummins when I bought this truck. i spent hours online and most people said 5000lbs would be nothing for a 360 3/4 ton. I thought I could save a few grand and now wishing I would have just bought something I know would handle any load i want to tow. O well always another day and another dollar spent. One queston...My truck has a factory goose neck hitch, Why would they put this in a truck with such a tall gear knowing that most likley it would be used for towing?

 

Id guess your truck to be about 5800lbs. Easy way to find out, go to a dump & put it on the scales.
Edit - Unless your carrying something real heavy in the bed we cant see

My V10 tips the scales at 6050lbs with full tank of gas which is 35gal tank.
It is a reg cab, long box, but it came factory with plow, tow & camper packages. Sits on the 3500 frame & has bigger springs up front as well as the extra set of leaf springs in the back & rear swaybars. Ive had it on the scales a few times at the dump.

CTD same configuration as mine is about 6800lbs, QC just over 7100lbs.

4.10s would be the way to go
Id check the plenum to see if you have a leak, can cost a fair bit of power.