The m819 CAN pick/swing 10,000 lb. WITHOUT boom supports on out riggers, 20,000 lb. WITH boom supports, I have lifted over the 10,000 lb. limit over the rear without the out riggers, the pick was about 5' off the back, no swing, the front tires never went lite.
The m819 is a awesome working wrecker, can do a HEAVY rear lift tow with the front tires never going lite, NOT like the standard military wrecker, with the way it is set up, ALL the weight from the rear trunion forward is counter weight ( crane, ect.) the m819 has 26' of boom, the really only down side of a m819 as with ALL military wreckers is that the boom does not have enough elevation, so for a heavy lift off the side with all the boom sucked in, short rigging is called for. It is a very under rated as far as lifts go, with a short boom, on out riggers, a good hoist motor and good boom hoist cylinder, I could see a 16,000 lb. pick, where bending of the boom would come in would be trying to a HEAVY pick out on the outer extension, or on the first extension out more then a few feet with a lowered boom, with the boom up as far as it can go, I do not see much of a issue. Remember, CAUTION is the name of the game, In order to use the truck to its max you NEED to KNOW the truck, not just jump in/on and start pulling levers. I would start out lifting some weight, see how she handles, see some limits, then work the weight up to the needed lift weight, if at any time you get the felling or see that that is as much as you can do. then stop and set that point as the MAX. weight that you can do SAFELY without tearing up the truck or the load.
I have had my m819 for 10 years, I believe I could do what you are asking to be done with my truck, though if asked to, I would use BRAND NEW hoist cable, go though the pump, not that either is bad now, just with MAXING out the truck, I would want as much edge as possible.
if you want to talk m819, call me.