2004 Dodge Caravan transmission

What observations exactly make you say it's going into reverse? Does it actually switch from "drive" to "reverse" without you touching anything?

"put in reverse it goes in reverse for a minute without touching, It goes forward"

You can see why I'm confused. If the wheels are still off, use a screwdriver or punch through one of the cooling slots in one of the rotors to prevent it from turning, then just watch the other side. If the van has anti-lock brakes with traction control, you'll have to turn that off to keep it from engaging. Look at the gear indicator on the dash. If you have multiple lights, a different light for each gear, look if they're all lit up. If you have a single letter that shows up, see if that is blank. Either condition indicates a problem with the range selector switch. It could be unplugged or misadjusted. Any electrical problem including anything with the range selector switch will send the Transmission Computer into "limp" mode. It will stay in second gear when in drive, but reverse, neutral, and park will still work. A lot of people get confused when the transmission defaults to limp mode after they've been driving for a while. It will bang back to second gear and stay there.

Also look at the shifter cable and its adjustment. You can disconnect it at the transmission end, then do the shifting by hand at the lever on the transmission. If that solves the problem, check for a misadjusted cable and that its bracket didn't get bent when the transmission was removed.

Once the transmission goes into limp mode, there will be a diagnostic fault code in that computer related to the cause. You'll need a scanner to read transmission codes. Simple code readers only read Engine Computer codes.

If nothing has worked up to this point, you'll need the scanner to view live data. It will show which gear the Transmission Computer thinks you selected. If the scanner doesn't indicate the gear you selected, suspect the range selector switch or a computer problem. Park, reverse, and neutral are selected manually with the shift lever and cable. Drive is too, but first, third, and fourth are shifted electrically by the computer through the shift solenoids. Be sure the connector pins are clean and making good contact on that solenoid pack too. Wiggle on the plug. If something changes when you do that, check for a stretched or corroded terminal in that plug.

736 - Gear ratio error in reverse
846 - 2 / 4 pressure switch sense circuit
PO7000 - No listing for this code. Could that be P700? Code 700 in the Engine Computer just means there are codes in the Transmission Computer.

There are pages of diagnostic steps for each of these codes. Unfortunately I am not able to copy and paste them. Your best bet is to get a copy of the manufacturer's service manual, but there are separate manuals for Transmission Diagnostics and other manuals for other systems. EBay is a good place to look for them. The problem is most of the steps involve using Chrysler's DRB3 scanner. You can do some tests without the scanner, and at least the book will tell you what tests need to be done.