if you had more than a 4" lift on it then yeah id go with blocks. but its really not a big difference between the 4" lift and stock 3/4 ton rear springs. i blew my rear end bout 5 years ago and i stuffed a rear axle and leaf springs from a 4wd tahoe with posi. and it actually brought my truck up...
when its in park it makes a bad grinding noise like possibly the torque converter. and when the trans is cold. shift fine as soon as it gets warm is when it shifts bad, the fluid and filter are bout a year old. only put bout 2500 to 3000 miles a year on the truck total. im guessing its done lol.