IMO it's easier to upgrade a TV than to upgrade a TT/Toy Hauler because you didn't get the one you wanted in the first place... New RVs depreciate faster & take longer to sell, especially off season... Therefore I recommend getting the toy hauler you want, within reason, and then upgrade your TV when you have time.
If you can sell/buy FSBO on CL, etc. you may be able to break-even. In 2013 I found a 2 year-old 2011 Ram 2500 CC w/5.7 Hemi for $14K. With the same 5.7 Hemi as the Durango it tows my 8,000 lb. TT (15,000 GCVW) throughout the Smoky Mountains with ease.
The engine is not the problem... The BIG difference is that the 2500 has a payload of 3,000. Our 6,500 (empty) TT has an empty tongue of 650. However, ready-to-camp the tongue weighs 1100+. Add our family of 5 (700) and we're at 1800 payload before adding a single item to the PU bed. In our case we have added a fiberglass cap, bikes, kayaks, firewood, etc. so our payload is around 2,500 now...
2011 RAM 2500 ST Crew Cab 5.7 Hemi
2011 Primetime 3150BHD Touring Edition
Days camped in 2016-36
Days camped in 2015-37
; Days camped in 2014-31