I have a 2000 Ford F150 7700 lb payload 4 x 4 truck. It has about 50,000 miles on it most of which is light highway use. I occasionally tow my boat, race cars etc with it. I don't plow snow with it. Recently the transmission has repeatedly held in 1st gear way way tool long when I first start to drive it. Now recently it has taken about 4 miles of driving before the converter locks up. After the truck is driven further and gets warmer it acts normal. I have heard that these trannys are quirky. I have also heard that Ford dealers have a fluid flush system where they flush out all the old ATF fluid, including what is in the converter, and pump in new fluid. I am told it is night and day after it is done. I think the dealers get over $100 for the flush. My tranny is definitely acting abnormal. I bought a filter and the Mercon V fluid to do a fluid & filter change, but I doubt I will be able to drain the converter. I think it holds something like 16 quarts and Mercon V aint cheap! I am not sure what model transmission I have. Any thoughts welcome. Thanks, Peter.