I need help asap!!

[nssj2]

I'd put money on a ujoint or your front driveshaft is toast. Makes sense because after filling the truck up (21 gallons), you're adding weight which is ever so slightly changing driveline angles. Check driveshafts for play, and if you see a lot of grease where your front driveshaft meets your transfer case, remove it for your quick fix. WARNING: your truck will creep in park with no front driveshaft.