We have 4 classes and different rules.
The stock class,(now renamed "street legal" class as most trucks are nowhere near stock), which I run, rules are as follows:
Engine used must have been available in that make/model year.
6500 weight limit with driver (they are thinking of creating a separate class for diesels as some extra/quad cabs are over this weight stock).
No NOS!
Cam2 racing fuel is allowed.
500 Cubic Inch Limit on engine (this rule is subject to change due to the 8.1 L popularity in newer trucks).
Dual rear wheel axles can only run one tire per side in the rear.
No solid lifter cams (hydraulic roller cams are allowed).
Single Carb rated at no MORE than 750 CFM (double pumpers are allowed), stock EFI setup (you can chip them and put higher flow injectors, but stock plenum, throttle bore, and pump must be used), or non-turbo diesels (there is going to be a separate class for turbo diesels/turbo gas so the turbos don't kick the naturally aspirated butts).
Tires must be DOT approved and uncut (no limit on size or width).
Driveshaft loops must be installed w/u-joint blowout shields on the pinion and t-case ends.
Autos MUST have a tranny blanket.
Manuals MUST have an SFI approved flywheel and a "scattershield" must be used (scattershield is any device designed to contain an exploding clutch).
Lift kits are allowed but not recommended
Rear end can be blocked (to limit suspension travel), but the frontend cannot.
Driver must wear an approved helmet, full length pants, full length shirt (no t-shirts or muscle shirts), and SEATBELT (seatbelt must function properly and be mounted securely).
The truck must be equipped with a fire extinquisher.
Weight may be added to the truck, but it must be secured, and no weight added forward of the front axle (if any object from the truck is dropped/falls off during the pull, you are disqualified).
Hitch height is limited to 26" high or lower (no "trick" or levered hitches are allowed.
Hitch must fasten securely to the frame and have a 3" MINIMUM diameter to allow the sled hook to go through.
If a reciever style hitch is used, the lock pin must be a minimum of 5/8" diameter hardened steel.
There are more, but this is from memory.