[brian_]

I was thinking if I take out the exhaust system and the fuel tank I feel the undercarriage should be big enough for a Tesla P100 Battery Pack. This van has a nice high riding height so ground clearance shouldn't be an issue.

Great if you can do it, but the volume of the fuel tank is 76 L (2.7 cubic feet) and the muffler is likely less than 30 L (1 cu ft). The Tesla Model S/X modules are 16 L (0.55 cu ft) each, and a P100 pack has 16 of them for a total of 256 L (9 cu ft). If you can find reasonable places to put the modules, they're likely to hang way down below all of the underfloor parts and structure that will be in the way, because they're much larger than the parts that are being taken out.

 

[brian_]

It has currently a 3.9 L LZ9 V6 Engine and a 4-speed 4T65-E automatic transmission.
...
My main concern, is this car's electronics to NEW, the transmission is a computer controlled transmisson and I don't know if Electric Conversions can make a computer controlled trans work or if I need to swap the trans for something NON-computer controlled. or is there a motor out there not to expensive that will connect to the front drive shafts like the Tesla Motor does via it's gearbox on the front of my Rav4 EV.

If you're using a low-voltage motor and need a multi-speed transmission, I can see the problem; an automatic is unlikely to be worth the substantial effort to adapt. Unfortunately a manual transmission wouldn't be an easy fix, because the Uplander isn't designed to accommodate a shifter or a clutch pedal.

If the plan is to salvage an EV motor (such as a Tesla, Leaf, etc.), then the obvious solution is to use the transaxle that comes with the motor.