I towed a 12 foot dual axle enclosed U-haul with my 72 K5 when I moved 70 miles away...wasn't the greatest idea..it pulled it fine...short wheelbase sucked though--it swayed and weaved constantly,like it had no "straight ahead" position like it did unloaded...top speed was limited to 50 mph ,maybe 55,after that it just felt too squirrely to handle without great pucker factor..
The trailer had no brakes,and I had maybe 1 ton of furniture and other stuff in each load..
It made 2 trips back and forth OK,but I don't think I'd want to do it again with a K5...a Suburban or 3/4 ,1 ton long wheelbase would have been a lot better..(or I could have just rented a C-60 box truck for about the same money,and hauled everything in one trip!)..
One reason I sold a minty '78 Rockwood camper I had,based on a 1 ton G-30 chassis,was the fact it had a 110" wheelbase..why they didn't use the 125" "long van" wheelbase I couldn't understand..the thing only had 58K on it,I drove it to Nashville TN and back,and it too,felt like it just wanted to go right or left,not straight ahead,most of the time--after you got used to it being so "touchy" you could get it up to 70+ mph,but if you had to make a sudden manuver or stop,you'd be in trouble....it also rode like a dump truck,very harsh springs and bouncy...I would have been scared to try towing anything with it...