Need advice on buying new vehicle

Hello, I just joined the forum and I am in need of some opinions! :) I am 16 years old and I'm in a bit of a predicament. My first car was a 1961 Ford Galaxie that I bought for $1000 but I did not get it running in time for my driver's test. Luckily I was given a 1985 Oldsmobile Delta 88 that is in pretty good condition. I then saved up for a truck and I bought a 1995 f150 for $2000. After a couple months the clutch went in the truck and found a bunch more issues so I sold it for $900. After that loss I borrowed money from my grandfather and bought a 2007 ram 1500 which I am currently driving. I just finished paying the truck off and I am looking to get something new. I can get $7000 for the Dodge from someone I know. Some ideas that I am considering are a pre 2006 VW Jetta TDI because of their crazy MPG, swapping the 307 in the oldsmobile for a rebuilt 350 and manual transmission and use the money from selling my truck for fixing it up, or selling the Dodge and Oldsmobile and buying a beater car and and a dirt bike and saving the rest of the money. Any input will be greatly appreciated as I am stressing out trying to figure out what to do! :1zhelp: