If its a 99-04 its probably a rear main seal or rear main seal housing. Its cheaper to get the housing that comes with the gasket, new bolts, and the seal already installed then it is to get the rear main seal and cover gasket. If its an 05+ its probably the oil pan leaking.

 

Has the oil pan been off or oil pump been replaced? Possibly forgot to dab silicone in corners of oil pan gasket?

 

no the oil pan has not been off. i did however just install LT headers and i did not seat the dipstick properly and cut the o-ring. the rear main may be leaking as well but i need to fix the dipstick leak first and pressure wash the truck and see if i have oil their as well.