sending unit

Im now going thru this issue.i bot one from a well known name in fuel and put it in yesterday,,,before I installed it, I put it under the car and hooked the wires to it and ran it thru the paces..it worked but not accurate..full on the sender said 3/4 on the tank..i did a little adjusting and got it a little better,then installed it in the tank..tank was completely empty ,,I put 5 gallons in and no response at the gauge.put in five [10 total]still nothing..I then grounded the gauge line and it went past full..then I used jumpers to make sure I was getting [contact] grounds at the sender and on the ground wire and no change...so its in like its supposed to be cept not working right..now my only conclusion is a float that's stuck,although I dont see how that could happen,or a float that's heavy..[cracked full of gas ..etc...ill have to drain it [AGAIN] and try to see whats going on..i looked at a lot of senders and came to the conclusion that they all look alike..no matter who you bot it from ...looks like one manuf and every one else sells them under the guise of its their product.no issues with leaks ..the gasket was .015 thicker than a well known but the new ring was 020 thinner..use your old ring ..far better product ..any thots..j