Earlier Ford trucks had it too...thr tranny was the topic of this post...my '92 F250 would go into "limp home" mode when the vss module went out and also when the fluid level got too low. It would upshift really HARD and the overdrive lamp would blink to tell you it was in "limp home" mode. Codes would also show up when I took it in for repair....Can't really remember what they did...maybe changed fluid. Finally had to have the tranny overhauled - at about 150,000 miles. Never had the problem again.