I Am having Transmission Problems with my 2000 Jeep Wrangler w/ an automatic?

I'm 16 and just got this jeep a couple of months ago. I love it and its a blast to drive but i have been having some problems with it. When im driving down the road, accelerating from a red light, my transmission seems to almost stick in what i think is second gear. When this happens, my car starts to slow down and the RPMs go way up to around 6 or 7. But after pressing on the gas more or letting go of the gas, it shifts into 3rd and its fine. This only happens when accelerating. I don't hear any grinding or clanks so i don't have a clue what is going on. Also, When ever i have my left turning signal on, and i touch the brake, the signal sticks and stays on until i let go of the brake. Its starting to get quite irritating, but it doesn't happen all the time. Oh and by the way, the Jeep aka (Joe), has almost 140,000 miles on him. Do you think that after that many miles my transmission is just getting old? I have checked all the fluids and everything is fine. I also checked under the hood to see if I could hear a vacuum hose that was broken/detached. I don't know what else to do besides take it to a mechanic