Could have bad synchros in the transmission... The NV3550 is a fairly stout transmission, and would definitely be worth repairing if you aren't planning a motor swap any time soon.
You say that the transmission just started doing this,and is more likely to do it after sitting overnight... I didn't look to see where you live, but these transmissions are notorious for getting really "stiff" when they are cold. Does the problem go away completely once the transmission warms up a bit? You say that the transmission has 167,000 miles on it, do you know what the condition of the fluid inside is? (Did you change it when you bought it?) If not, I would start there, and see if that helps at all. If not, a reputable transmission shop should be able to help you diagnose your problem for sure. If you can't find a good recommendation from someone you know, take the Jeep in to a couple places before you decide what repairs to do.
Originally Posted by Scout
I like "prick".
Go ahead...quote me on that.
"Hold my beer while I kiss your girlfriend... you have to be good for something"
If you have to ask what it is or what it does, you don't need it, and you will need help to install it!