It'd be a really good idea to get the gauges installed before doing anything else. And when you do install the plate or slide it, make sure your gov arm is adjusted properly. Instructions are here: http://www.piersdiesel.com/TechLeverAdj.htm
You'll be amazed at ther difference in power. Try to avoid getting on the go pedal too much with the TC locked up and your tranny will last longer.

 

change your fuel filter and slide your stock plate full forward after you get atleast a pyro. You would prolly be ok without a pyro, but you will eventualy need it anyhow. you will get the modification bug after that so dont blame me after you step up to a bigger plate then get a boost elbow.

 

Do the govenor springs too if youre gonna do a plate

 

Go to the top of the page, click on articals. then click on 2nd gen artical then click on modifiying you 12v p pump. It is the best artical Iv seen explaining the afc and how to adjust it for your plate. Piers diesel research web site has a good one for the 3k gsk and one on where to install your pyro. I went to the dtt site and could not find the artical on trans. oil pressure that used to be there. I have it printed out somewhere. I will try to find it.
A bad return valve can also give lack of power. It is built into the banjo fitting where the return line bolts to the injector pump. I think it is about $30 or so if you know where to get it. It is a known problem on the P pump. I carry a spare with me all the time. That price could be wrong. I have not looked at one for about 5 years.