ya it could be the timing chain, but thats alot of work, so B 4 u do that, id check your timing, how many degres it is, and wut do the plugs look like, beacuse if your running fat on the fule and retarded on the timing, you can get a backfire, but it does sound like the timing is off, but i havent had that problem with out the chain being hella lose and when its that loose when u first start your truck it will slap for a lil bit, and under a loal it will slap also
