Tow rig? Keep my 1/2ton or new dmax?
 

Can i make my 09 5.3 6l80 4x4 with 3.42 gears be a reliable tow rig or dump it and buy a new duramax? A dealer by me still has a new 11 yes 11 silverado LT ecsb with a duramax discounted down to 38k from 51k. Im gonna be towing a 30' travel trailer around 8000lbs through Colorado mountains ect. Steep hills! Any input would be appreciated.

Your combo will likely work but the dmax will work much better. How other gear are you planning in carrying? At 8,000 pounds and only 3.42 gears you have to be close to your max GCVW already.

Very close to the max. I'm worried about stopping as much a I am about getting up the hills. What could I do to my truck to make it a tow rig or is it a lost cause?

Not necessarily a lost cause. Depends on why you want to do. Swapping to 4.10 gears will definitely help you get up the hills and a big brake kit will help you stay under control on the way back down. If the travel trailer doesn't already have disc brakes you could do swap those in as well. You should add a big transmission cooler also.
A DMax is pretty much get in and go by comparison. You'll likely get better mileage with the DMax as well to offset the higher fuel cost.

What he said. No way I'd tow that much without all the above mods to a 5.3, so the cost comparison will be interesting.

If I'm gonna get 8mpg it's gonna make up the difference in truck cost real quick. Plus all the upgrade i will need to make. What will a tuned and full exhaust lml duramax get for mileage?

Full exhaust meaning factory exhaust or you replace the exhaust and delete the DPF?

Turbo back exhaust dpf delete and custom tune.

I'd get the Dmax, I'd be worried about going down a hill or something while pulling that trailer and someone pulling out infront of you... Or if you get into stop and go traffic, I would think the D-max would be better for pulling,stopping,its newer so you can keep it longer and you' probably can get decent MPG after a tune..

Go Dmax for that towing setup. Better in all aspects that you talked about using the truck.