Transmission and gauges

[mitchethekid]

Hello.
I have a few questions that I need some help on. I have a '98 328I. For some time when shifting from 2nd to 3rd or from 4th to 3rd, the car shifts into 5th. I replaced all the shift rod bushings to no avail. I have read that the dent pins which screw into the top of the transmission could be the problem. I work at a non-BMW dealership and the tech guys are perplexed. They seem to think that it is an internal issue (in the trans itself) but can't seem to find a schematic of the transmission. Can anyone in the group offer some advise?
The next question is; if I want to install some aftermarket gauges that fit into an A pillar pod, how to I route the wires so they do not show and where do I tap into the lights so the gauge lights come on when I turn on the headlamps?
Lastly, I have been told that my serpentine belt tensioner has failed but it is original and mechanical and has been replaced by a hydrolic tensioner. What parts to I need to buy to replace it. I have read that one needs the new tensioner and some sort of "kit" to go along with it. And, of course, what steps are involved in replacing it?
My sincere thanks to all who offer to help.