Is there a company that makes a unit to work with my th400 and np203 set-up.  

Not that I am aware of but it would be far cheaper and more effective to adapt in a OD tranny even if one was available. A 700R4 would be the ticket here because it does not need a computer to work. A 4L80 is a THM400 with OD added to it but it has a electronic valve body. Properly build a 700R4 is a sturdy tranny and can even handle a big block. Where people trash them is they lift them and install big tires and not regear axle and lug tranny on converter a lot and slow bake it. The 700R4 has a much lower first gear than a THM400 (3.06 vs 2.48) and it can launch a tall combo better (giving you false sense that all is well) but then it suffers in upper gears when effective drive ratio get to tall and it rides converter stall a lot which makes heat and slow bakes tranny.

*** I might add with full time 4x4 drive your are losing about 10 to 15% MPG from drive system so OD is not going to be a magic solution for you anyway.  

The Klune-V will work with your setup. But you do need to decide if it is really the best answer. You can swap in an OD tranny easier and cheaper in most cases.  

thought  there might be something that was an easy bolt on, i have wanted a 700r4 but everyone says they suck for offroad or high output engines.  right now i have a basicly stock 350, th400 ,np 203.  When i get around to rebuilding the engine it will have around 325-350 hp and about 375-400 lbs trq.  Im trying to get the most out of my tranny/t-case setup in order to budget some more cash into some corporate 14 bolt axels to replace my pathetic 10bolt/12 bolt set-up.  It is looking like my best option is to double my 203 with a 205 and keep my th400 to make up for the weak ass 2to 1 low.  Does anyone make a kit to regear the 203 and/or even rebuild the th400 and put in a deeper 1st gear.  

It never fails to amaze me how people say 700R4 are terrible off road trannies. It is arguably one of the best trannies made by GM in its 87 on form. It is not computer controlled so it is easy to swap and has a deeper first and second gear and OD too. Tell you what, you find those people that actually blew one up and look at their axle ratio and tires size combo and tranny cooling and you will find the real reason they failed. Typically somebody lifts truck and put big tires on it and has stock tall axle ratios still. (BTW, even a 4.10 is not by any means a deep or proper gear with 35's on)  The deep first gear on 700R4 helps launch this mess but as it upshift the tranny starts to lug and overheats and fails because effective ratio is too tall. With a proper axle ratio for tire size (you want tire diameter divided by axle ratio to be less than 7.5 with a 700R4 to make best use of all gear ratios in it) and a aux tranny cooler too (no need to go overboard with size) and it will hold up just fine. One more thing, stay away from shift kits as they bang the internal sprags really hard and can cause them to fail with time ( the shift is modulated for a reason) BTW a properly built 700R4 can handle over 700 HP.  

Are you looking for over drive or under drive? They are two totally different things. Gear vendors sells overdrive units. If you want an underdrive unit, then you can bolt a Klune-v or Northwest Fabworks Black box between your tranny or t-case. As you already stated, you can go with a 203/205 doubler (I'm working on this right now). There used to be a company that made a 3:1 kit for the np203 but they are no longer in business. JB conversions does make a 3:1 kit for the Np205 though.  

large box vans and some class A motorcoaches had a straight cut planetatry gear, in the TH400's, sometimes you can get used ones from all trans parts. I dont know what the reduction is exactly but It is much lower than the passenger planetaries

tereflex has a 3:1 for the 205 also, at least they did, I have one.
I have a gear vendor unit in my 85 extended cab chevy dually, 6.5TD w/th 400 and 205. these are awesome, operates like a 6 speed. a little long for a jeep though.

I thought they had a unit that replaced the backside of the 208-241 cases, from what sales was saying, this was 12 years back when I was looking and got one, I wasn't interested in the od in 4 wheel drive. got mine from Six States Distributors in Portland, Or. I still haven't managed to break it.  

overdrive unit would be better because it would allow me to gear dowm much more and still keep some highway use. ill check into the ones you suggested.