Why won't my trooper shift into 2nd gear and rpm is going really high

What is your question?

My 2001 Isuzu Trooper was parked for nearly a year inside my garage. I put a new battery in it and it started just fine. Let in run a while and drove it around the block a few times. The next day as I'm driving down the road I suddenly lose power, I tried getting back up to speed and the rpm would just sky rocket. I came to a stop sign and from there I could not shift into 2nd gear and rpm was still going high at about 4,000 rpm. The problem is now consistent. Is my transmission bad? Why did it run fine the first day and shift properly but not the second day?

What makes this problem better or worse?

When I put it into drive and try to shift into second gear

How long has your 2001 Isuzu Trooper had this problem?

A couple days now