[Zoomad75]

At least you got some idea of what direction you are going in. I'll take a crack at your questions, more should chime in soon.

1. I am shooting for a 6 in lift and 37in tires. Do I need custom drive shafts?
6 in is right at the limit for stock drive shafts. Some need to change at 6" some don't. Each truck is a little different, you are just going to have to cross that bridge once the lift is on.

2. What gears should I be running for best all round gas milage and torque?
With 37" tires you can all but forget about fuel economy. Just to be able to get those tires rolling you will need at least 4.56's by my calculations. 4.88's wouldn't be a bad choice to bump up the low end. Don't go with 4.10's. My truck with 35's and 3.73's is a dog, 4.10's and 37's is about the same. no 4.10s won't help fuel economy because you got to stand on the gas just to get the darn truck moving.

3. GM ZZ4 crate or 383 stroker crate or rebuild the 350 4 bolt main thats in it? Wide open choice here. You want low end torque. 383's are great for torque, it all depends if you want to build or buy. Shoot for a 300 hp range minimum with a nice flat torque curve.

4. I plan to keep my TH350 and 203. Is this a wise choice?
Stock, the TH350 is pretty strong but won't take a lot of beating without some fortification. Get it built by a good rebulider and have them beef it up. The 203 is ok, but it needs to have the part time kit added to it or else you will be in 4wd all the time (more fuel used and front end wear on the street). I'd find a 205, keep the 203 and get a doubler setup. It bolts the 203 rangebox between your TH350 and the 205 giving you an addtional 2:1 gear reduction before the 205. This makes up for the 205's only downside of it's 2:1 low range. You can have 4:1 compound low for better crawling and hill decents.

5. If I did trash the 203 will a 205 bolt in? If not whats my best choice?
See #4. Installing the 205 by itself would require a new tranny to TCase adapter for the 205.

I'd also think really hard about upgrading the rear axle to a 14bolt full floater. Most say 12 bolts are limited to 35's with careful throttle. 37's can be done on a 12 bolt but you better carry spare axle shafts. 14 bolts can be had for under $200 all day long, plus Detroit lockers are cheaper for a 14 bolt. The Dana 44 will also get strained with 37's and a heavy K10. You can upgrade to Chrome-moly axle shafts as a preventative measure but it's right at the limit. Might start looking for a D60. Keep an eye out at your base if they still have some old CUCV Chevy trucks. The trucks had D60's and 14bolts loaded with 4.56's and a detroit out back. The ambulance models had Trac-locs up front when the rest were open. They get auctioned off pretty regularly and it would be an easy swap.

Hope that helps and keep safe when you do ship out to Iraq!