Stuck in 4wd for 2 weeks. seems to be unstuck but doesn't go when in gear

What is your question?

Would not come out of 4wd for weeks. Now it is back in 2wd or so it seems but speedometer is reading 80mph when I know I am driving the speed limit or less and tach is at 3000 rpm. Also doesn't move when in gear sometimes but sometimes does this problem just started last night. Took me 2 hours to drive 1 mile to get it home because it didn't want to go. No leaks and makes a loudish rumble sound. It is my boyfriends truck, I am more mechanically inclined than. He is. I told him to stop driving it when it was stuck in 4wd he didn't listen to me. He wished he had listened now . I don't know about 4wd or much about transmissions but I have dropped one and reinstalled one before ona. Jeep to replace a freeze plug. My thoughts were trandfercase needed to be lubed and now tranny may have just blown completely can someone please help me out. I can probably fix it myself if I dont need any high priced specialized tools but I need to know where to start.. could the truck maybe have jumped time?