Both have about the same amount payload, tow ratings, gearing. Crewmax has 15" longer wheelbase over the Expy EL, but I doubt that will have any affect on stability. The Ecoboost has a broader torque curve so will maintain speeds at 2000-3000rpm compared to the naturally aspirated V8 2500-4500rpm. Both will work well and should be durable for hundreds of thousands of miles. I don't see any reason why a Tundra should perform poorly.
If you otherwise like your Expedition, I would focus on a couple things that could improve stability. Spend $100 on Grand Aero towing mirrors and keep enjoying.