In before the troller starts throwing stones.
4000 pounds shouldn't be much of a struggle for ANY of the V8s (or comparable engines) in the newer trucks. If you like your Tahoe except for the power, consider a newer one with the 5.3 and 6 speed tranny. BIG improvement over what you are currently driving.
In regards to the RAM, that 5.7 will tow it VERY well. Me personally, if I was only towing 4000 pounds, I would probably go EcoDiesel.
2012 RAM 3500 Laramie Longhorn DRW CC 4x4 Max Tow, Cummins HO, 60 gallon RDS aux fuel tank, Reese 18k Elite hitch
2003 Dodge Ram 3500 QC SB 4x4 Cummins HO NV5600 with Smarty JR, Jacobs EB (sold)
2002 Gulf Stream Sea Hawk 29FRB with Honda EV6010