The slowest car ever?

[palmtree]

I just bought my first volvo. 1980 wagon with the D24 engine. It is the slowest car I have ever driven. I'm not a lead foot -- but you have to be in this car. That said -- I like it. It has always started right up (so far anyway) and it runs pretty good. There isn't any rust on the car. That's pretty amazing for a car this age in Missouri. I'm not sure if it lived most of it's life in the desert or what.
The first thing I noticed besides being slow is that it really needs another gear or maybe two. It has the original 3 speed automatic. The tach doesn't work but it sounds like it is really revving at highway speeds. When driving down a pretty steep hill on the highway and I let my foot off the accelerator it will actuall slow down because it is revving so high. I guess the first big upgrade I would want to do is replace the transmission with something that has an overdrive. Any suggestions?
Thanks for this site. I have learned a great deal already by reading the old posts.
Brett