I'm looking to pick up a tow vehicle. The trailer is a 20ft enclosed so I'm looking for a pickup truck, not a suburban/excursion, etc. I want something that has got a real strong transmission. I'd rather not have to replace it every 3 years. That being said, I think it would be smartest to buy a truck that hasn't been used to tow with in the past. I'd like to keep the cost under 10k. I was thinking an F150/250 or a chevy/gmc 2500. I'm no truck guy so I know nothing about which models are best for towing, which are weak, and how they differ from year to year. Can anyone provide some advice?

Thanks