Trailer brakes. Transmission cooler. Transmission shift kit upgrade, fresh fluids. Semi-metallic brake pads. Emergency brake 100% perfect function. Sway bar(s). Coil over shocks on the rear. Start off in low when ever coming from a dead stop. Have that hand on the shifter when traffic gets clustered. Check transmission color durning long haul stops. A massive radiator upgrade may be in order, if steep grades, slow traffic. Also air flow issue becomes enhanced as well due to increased loads. Trailer spare(s) & checking the load rating of the car tires doing the pulling.