I would not recommend a gen 1 ST, here's why. With the availability of the gen 2 marked improvements have been made in these trucks, not just in handling but quality. I don't own a gen 2 but I am very familiar with gen1. I've had my truck for 11 years, with 130k, here's the rundown you should look out for.
1. transmission problems, in general if you keep this truck you will run into problems.
2. 4.0L sohc has known timing chain issues, be aware that it will require complete engine removal to get to right side.
3. Ford parts are expensive.
4. Ford technicians are poor at diagnosing problems related to transmission.
5. mpg for a truck is not bad but gets about 18mpg combination, with gas going up it's up to you.