fuel gauge goes down very fast whilst driving and then goes up to what it should be when stopped

Have the fuel sending unit checked-start here

ok thanks also seen similar problem on youtube guy has dodge caravan 2001 does the same plus more somebody suggested to check the return pipe for kinks could this be the case for my voyager limited thanks in advance and also is the fuel sending unit expensive

oh and almost forgot the car had a gas conversion and was sold to me without the gas or propane tank could this make any difference to my problem thank you for all of your advice and help

You need to open it up and check the float resistances could also be a wiring problem

ok thanks i shall get on it today and let you know