So the truck was fine this morning, but when I drove home for lunch it would be fine in drive for about 10 seconds and then it would rev up and not be in a gear. If I rev it up high then it slams in to a gear and then slips again (i've only done this twice - once by accident and once to confirm). If i put it in 1 or 2 then I can drive around just fine.

What do you all think, minor problem or major? I know nothing about transmissions.

 

Have you checked the fluid? Is the OD light blinking?