I have an '87 3/4 chevy that I had a four inch lift in with 33 inch tires. It looked a little funny but acceptable. Then I added a two inch body lift and it looked really funny. I don't think it looks good at all. I put 36s on it and it looks awesome now. In my opinion you need 35s or 36s on a 6 inch lift. In my experience if you want the truck to look it's best you need to use the largest size tire possible for your lift.
I agree fully.. 6" and 33's just doesnt look right.. I happen to love BFG M/T 33's.. they're a great all purpose tire and a perfect compromise when it comes to size.. but they look puny with 6".. I think they look perfect with 3-3.5" of lift
on my truck which has the stock lift now (77 K20) the 33's look big, almost too big.. i plan to go with a 3-4" lift soon to even it out..
Most of the trucks i see with 33's look best with under 4 inchse of lift....6inches with 33's looks like baby doughnuts on a monster rig..if you go above 4 I say jump to some 35's...this week I converted my 82 long bed to a heavy half and the leafsprings jacked the pack up 3-3.5inches...with P235's (29inch) tires underneath they look like some little baby's so i am gonna go up to a 31-33inch tire. Btw this conversion has stiffened the rear end like a rock and bumps and the whole rear end jumps off the road...not a suggestion if you wish your truck to ride like a car. We are loading the 82 down with heavy trailer anyway so it should be fine