ECM problems.
 

I purchased a 1994 Tioga motorhome on a Ford E350 Chassis last October and have had some fun fixing it up into a dependable motorhome.
My problem: When purchased the engine would stumble and hesitate at stop lights. This was eventually diagnosed at my local Ford dealer and he suggested that I change the ECM. I did that. Three weeks later on vacation the engine severely lost power when climbing a 6% grade in CA. The local Ford dealer in that area said that the ECM had failed because it was the wrong one for our application (motorhome). The new ECM was airfreighted to us while we sat for 4 days. Since then the rig has performed very well.
My question to you is: How problematic are these ECMs since all of them are not stocked by Ford and I must rely on rebuilt ECMs from someplace in Texas. Also Is there an aftermarket ECM for my application that will provide a bit better fuel economy. I currently get 9.5 - 10.0 MPG on a 10,500 lb. vehicle.