Kekule,
You have 150,000 miles on the truck, no idea of it's history, a valve hanging up already and you're asking what to do.
First of all, the changing of the filter is not what is hard on an old ******, it is the new fluid. All the filter is going to do is to pick up junk out of the oil, which is good. I am a big believer in the ****** flush, especially from B&G, but you have way too many miles on your truck to start doing that now, it will kill you.
Bottom line, you own the truck, just use some common sence, do at least a fluid change, at best a fluid and filter change and see how it goes. What ever you do at this time is a little bit of a roll of the dice, and you have to do it, if for no other reason then the sticky valve body.
It is good that you are asking for info, but don't let everybody confuse you and cause you to wait or worse yet do nothing. At some point, in your case, sooner then later, your ****** is going to take a s--- because of the high mileage so try whatever you can to stretch it out for as long as you can.
Good luck,
Mike J.