Fix up older truck or save for new?

Im in a dilemma where I can't decide if I should fix up my current truck or save for a newer one later down the road. A lil background about myself. I am 22, currently in school studying Fire Technology and will be in the Academy within the next year or two. I make an honest student income as a Valet. Nothing worth bragging about!

My truck right now is a 2003 Dodge ram 1500 hemi 4x4. To fix it up, I need a paint job, tires, ball joints, cv axles and a few little things. I came up with a sum of $5k to fix it up. To pay for it, I would get a personal loan or a line of credit. I know its bad to borrow money for that but I want to use it more to build credit and be able to keep my money. The truck has 130k miles and is worth about $8-9k on KBB. I feel it is mechanically sound. I have replaced the rear end with a TRU TRAC and have done a few other things. Is it worth dropping another $5k to make it last until I can afford the truck I really want after I start my career?

My second option is to just run the truck into the ground and sell/ trade it in for a 2010-2012 ram 1500 2wd truck. I would only want to spend $20k on it then add the lift, tires, etc. I would be completely satisfied with this truck however, my dream truck is a 2500 cummins diesel.

Im leaning towards fixing the truck up but the thought of spending $5k on a truck that is worth only $8k makes me nervous. I know most of you have gone through various cars and have probably been in the same situation at some point. What are your opinions?