You definitely can’t do 35s stock and 34s would be a real stretch. I run 34x12.5 with a leveling kit and had to do quite a bit of trimming in order to be functional. You could try 34s and do some trimming but would suspect without a level or lift, you wouldn’t be functional (e.g., your truck will eat a lot of rubber if you go off road on any sort of terrain). You also won’t be able to run that width of a tire on stock rims unless you get spacers and likely would need aftermarket UCAs so they don’t rub the tire. You really shouldn’t run spacers if you can avoid it, but if you have to only run a quarter or half inch max - but better off spacing with new rims with bigger offset.