is it common on a 4.9 for it to leak alot of coolant at about 160,000 miles. my only guesses are a head gasket or a waterpump

Look at the water pump first.....and inspect it. The waterpumps on these cars do tend to go...from what Ive seen.

i could still be looseing coolant from a headgasket issue , mine leaks on the rear bank between cyl 4-6 to the outside (luckily) . But ive fixed other things and added coolant suppliment to it so if i am looseing coolant it isnt enough to notice

but really it could be the waterpump , they have a pee port in the bottom when the pump starts to go .

also make sure to check all your heater lines esp the tee that resides above the rear valve cover towards the center of the valve cover , made of plastic this thing turns into a crispy cookie after 10 years of warm up and cool down , they start to leak slowly then one day when you got the foot to the floor mergeing into the highway itll explode