A 99 4R 4x4 is only 3400 lbs? A GX is a lot more than +1000 lbs. My stock 05 GX with KDSS (no hitch) hit the scale at 4950 lbs. with near empty fuel tank and no passengers. I towed a big block 22' Sea Ray that scaled almost identically to your Chaparral with a 91 Pathfinder 4x4 manual trans. (3.0 V6 w/ 180 ft. lbs. of torgue, around 150 h.p.). I think that was around 3500 curb weight and it towed fine. Never felt like the tail was wagging the dog, as it did flat towing my FJ40. Did a number of mountain pass trips from NV up into western Canada. It was pedal to the metal a lot, but it worked. Actually got better mpg at higher altitudes even though powered output was clearly reduced. I think you'll be good if your 99 is as light as you say ... I don't know, but I'm skeptical. GX should do even better. Enjoy!