Recreational Vehicle Lpg Tank Valve/gauge problems of the 2003 Toyota RAV4

While driving the highway in my Rav4, it randomly bogs down or stalls out completely. You have to steer over to the side of the highway because it loses power and the gauges go whacky on you. Sometimes it shuts off and sometimes it just loses power and when you put it in park and shut it off, it will eventually "go again". You can be driving 55 one second and it stalls out to 3 mph the next second without any indication that it is going to happen. Toyota said they could replace the ecm if it was before 150,000 miles, which it was not. They told me they won't do anything after 150,000 miles, not even meet me half way to pay to replace it. Its an obvious problem if they sent a letter out. I've had it to three repair (including a Toyota dealer) shops and none of their 'computer checks' show anything is wrong with the car. How do you fix something if you don't know what is wrong with it? they have done tune ups, replaced the oxygen sensor and minor adjustments to no help. I've spent over $1,000 in repairs for "nothing" -or maybe this is it. I drive 2-lane highways and it is going to strand me someplace, if I don't get rear-ended by a semi-truck before that happens. I am afraid to drive it and I am afraid to let my teenagers drive it. The car is still in beautiful shape, has been garaged most of its life, has had regular oil changes, etc. And basically its worthless to me. I can't sell it outright with this problem that no one can find because I couldn't handle if someone got hurt, and I can't afford to replace it. I bought a Toyota because of their long life (everyone told me they will last 300,00 miles) but they have very much disappointed me in their customer service. What is it going to take, someone to get killed for them to realize that they have a known problem? why won't they fix it after 150,000 miles? it doesn't make any sense.