I just posted in your other thread

2500rpm @ 100kph does sound like it's in 3rd. Regarding the auto not going into 4th, is it *really* slow & doughy on takeoff? Because it might be in Limp Home Mode. Falcon BTR autos have this feature to potentially save the gearbox when something goes wrong in the car. Unfortunately many non-safety-related things can send a box into Limp Home Mode. Firstly check your ED's electrical system for any dodgy earths (battery terminals, stereo, relays, fusebox), and if everything appears good there, take it to an auto specialist who knows the BTR box and get them check it out.
But, if it clearly goes through 1st, 2nd, 3rd but not into 4th, it may be something else like the S7 solenoid.
Almost stalling upon braking/stopping could be due to the ISC and/or the TPS? ISC is the Idle Screw Controller, it's a cylinder thingy that's attached to the throttle body. This often collects gunk in it and fails. The TPS is the Throttle Position Sensor, also located on the throttle body (you should see two black plugs with 3 wires each - red green & black from memory - stemming from the throttle body). Maybe trying a replacement set of TPS' and/or ISC (if cleaning the ISC doesn't do anything) could solve the stalling issue. If the TPS is dodgy that may also address the auto's Limp Home Mode problem.
As for LPG, have a read through this thread -
viewtopic.php?f=2&t=1580I recently had my EF wagon converted to gas, and I strongly suggest that you get it done at a reputable LPG fitter who uses the same system that came out as a factory option from Ford, or similar, such as Parnell. I had a lot of problems with my conversion when I went to a place that sold a little-known aftermarket system (I can't remember what system I had).
For wagons, go for a 3 x scuba tank setup that goes in the spare wheel well, and the spare wheel gets mounted in the right side of the cargo area.
And MAKE SURE you get the LPG system dyno-tuned by experienced dyno operators who know LPG. Driving around with a shit tune will guarantee you $$$ lost in the near future.
Before you look into LPG though, get the car running right first (fixing the auto's problem, and the stalling problem). Also consider how much you drive it as a daily, if it's only short kms such as 10kms a day, it will be a long time before the LPG system pays itself off and you may be better off sticking with petrol.
-Dave-