1999 Ford Explorer XLT V6 has a transmission problem. What do I do?

Before either junking the truck or spending an enormous amount of money on a new tranny, I'd like the help of the people on this forum on how to troubleshoot my transmission problem and to soak in the wisdom of y'all on this forum.

Today, for the first time, it took me about 30 minutes of messing around with the transmission lever to get the truck to go forward. Prior to that, it was slipping in the first couple of gears, but driving fine after that. The slipping got worse after rope-towing my wife's corolla. It would no longer "catch" in Drive, but if I shifted into 2nd and THEN into drive it worked fine. Now, as I mentioned, it works fine in reverse, but not in any of the forward gears. Here are the symptoms to help you help me figure this out:

1. The car works fine in reverse, but does not work in any of the forward gears
2. I finally DID get it to go forward (although I could hear "chugging" from the transmission) after about 30 minutes of shifting back and forth.
3. The temperature gauge on the dash reads COLD (could this have something to do with it?)
4. I had a couple of instances of a misfire in cylinder one a couple of days earlier. It has not recurred
5. There are no codes in the ECU and the Check Engine light is off

My questions:

1. Could a blown valve body gasket be the cause of all this trouble?
2. Is the dead temperature gauge a related issue?
3. What would my troubleshooting steps be to identify the problem?
4. In your opinion, would it be worthwhile replacing the tranny on this vehicle which has 144,000 miles on it? Aside from a non-functional driver's side door lock and under body rust, the truck is in excellent condition.
5. What do you think about replacing the tranny with a junkyard tranny for $200? Is it difficult to do?
6. If replacement is needed, what should I be paying to have it done?

Thanks in advance for your help. We are NOT loaded and it's important to fix this problem as inexpensively as possible.

John