I'm new to this forum, but thought I'd toss out possible options to consider. I spend a lot of time looking on Craigslist for low mileage older V8 trucks and SUVs to use as a towing vehicle. I found that there are a lot of them. It appears that a lot of owners want newer vehicles with a lot of bells and whistles. Thus, there are a lot of bargains on if you are willing to go without all the great technology that's available on newer vehicles. On modern engines, 100,000 miles is low mileage. It might not be too expensive to sell your small truck and buy a more appropriate vehicle with a V8 and a higher tow weight rating.
My other thought is, to do what you can to beef up your small truck. There are some things you can do to increase the hp, but not by much and there is a substantial cost (cold air intake, improved exhaust system, tuning chip). However, you might instead consider upgrading your shocks/struts to handle a heavy load. You might also consider whether air bags on the rear springs would help. Air bags are inexpensive and easy to install. Those suspension improvements may make your truck ride more rigid than you like without a load, but should make for an improved towing experience.
It probably goes without saying, but just in case........ It is critical that you have a good quality weight distribution with sway control hitch system that is designed for the tongue and trailer weights that you'll be towing.
Best wishes on your new adventure. Please keep the forum updated on what strategies you decide work the best for you and your significant other.