Instrument gremlins.

If your fuel gauge is working then the small stock voltage limiter behind the dash is working. The temp gauge issue is either can be anyhwre in the PC board, the temp gauge, then wires and bulkhead connector out to the sender, the sender itself, or the sender ground in the block. If you want to try to figure out the stock temp gauge, then disconnect the wire from the temp sender and connect it to a 12v test light; you should see a pulsing light. If so, then all is good to that point and it is just the sender. If not, then you have to work your way back into the instrument panel and find the problem.

The instrument lights out is often casued the dimmer rheostat in the headlight switch. Easy to replace the switch. There is an INST fuse in the fuse panel to check first though. The instrument ligths wiring is described in this thread: http://www.forabodiesonly.com/mopar/showthread.php?t=296230

If you speedo is reading 25 mph all the time, even stopped, then it is in the speedo itself. It's not clear about when it is doing this. Somone has fixed these and has posted on this forum somewhere, but replacement is the most common fix.