Ok, first of all, let me tell you I'm not judging you, and I'm sorry you got busted. I used to smoke weed....a lot of it, too. I never got busted with it, but came way too close once, so I quit. You're young, you made the mistake, and now you're paying the price. You've accepted that, you've vowed to change. That's good. I still have absolutely nothing against weed. I'd much rather meet a driver on the road that's been smoking than I would a drunk. Like Gallagher said, "A drunk pulls up to a stop sign, sees a semi coming 200 yds away, and says 'I can't make it'. A smoker pulls up, sees a semi a half mile away and says, 'Maybe I'll pull out tomorrow."
As for the drug tax stamp: The feds, under president Reagan, I believe, issued the law on drug tax stamps. Not all states adopted it, but most did. Basically, what it's all about is paying income tax for drug sales. I know, it's the dumbest thing. It's illegal to sell drugs, yet they legalize it by charging a tax on the money you make. If you purchase a drug tax stamp, you don't have to pay taxes on the money you make from it. If you don't, then that is where they can and will confiscate your vehicle, home, and anything else you used during the sale of drugs. Even though the Jeep was in your dad's name, they could have confiscated it if they had believed you were using it to sell drugs. They could still seize your parent's house (or yours, I missed who you lived with) because the drugs were found there, too. Normally, the cops won't go for an "intent to sell" charge unless the drugs are either in several packages (broken down into 1/4's and 1/2's), or there are other items which indicate it such as scales, baggies, etc. If you didn't have any scales, or packaging materials, then you most likely can beat that charge.
As for what happened when they pulled you over: Did they ask you to get out of your vehicle? If so, did you refuse (that's what it sounds like)? If you did refuse to get out when told to do so by a Law Enforcement Officer, that can be judged as refusing a direct order from an LEO and also as resisting arrest. Technically, once the cops redlight you, you are under arrest temporarily, regardless of why they redlighted you. So, anything you refuse to do for them once the lights come on is resisting arrest. Depending on the state, a refusal to obey an LEO is also probable cause for search and seizure, as they tend to see only someone with something to hide are the ones who resist.
Sucks, but you'll get over it. Look how many presidents, politicians, and other important people have admitted to smoking weed or worse. Hang in there, jump through their hoops, and put it behind you as best you can. You didn't kill anyone, though they may treat you that way for a while. You'll be fine, so long as you stick to your guns and keep on the straight and narrow.
'Nuff sed.