I hate to say it but you'll need a new transmission soon if you go that route. With 165,000 I'd say you need to get one anyways. As its not your DD I have a feeling that you'll be beating on it more than usual. Look around on here and you may be able to find a new used one thats been beefed up. I was able to get one for $400 in great condition. Then you can focus on doing a few mods. While you get a new transmission you should either go for 3.29 or 3.69. 3.29 seems to be the sweet spot but 3.69 is more of the tire roasting gearing people get.