Transmission problem

I have a 2004 Chevy S10 4x4 with a 4.3L V6 automatic. After a little four-wheeling in 4lo in 2nd gear (nothing too rough, or rougher than anything before), I took it back out on the high way in 2 hi in drive, and found she would not accelerate above 45 mph. Once that speed was met, it was as if it was in neutral, with the engine rpms jumping with the accelerator but as if not in gear. Other wise, she drives just fine, if I stay below 45. To get to 55, I have to put it in 3rd, and then the same thing happens all over, only 10 higher. Any help or advice would be greatly appreciated.
Thank you.

Welcome to AF.
Check fluid level.
Check under it for wire being off or damaged.
Any codes?
A good transmission/engine scanner should show the problem.
Post back code no.
MT