Need help

[tool 87]

I have a 87 supercab 4x4 5 speed and when i fill it up it reads full for a couple of miles then goes to half a tank then a few more miles it goes to empty but i can drive say 150 more miles i already replaced the fuel sending unit and the gauge cluster now what do i do

 

[Big Jim M]

So!

I have a 87 supercab 4x4 5 speed and when i fill it up it reads full for a couple of miles then goes to half a tank then a few more miles it goes to empty but i can drive say 150 more miles i already replaced the fuel sending unit and the gauge cluster now what do i do

So you pulled the tank and replaced the sendor in the tank? Sounds like there is a connection that isn't good.. OR the new sendor has went south... OR the float in the tank is sinking, caused by it taking on fuel!!
Big JIm

 

[tool 87]

yep brand new unit and it did the same thing as the old one so i am guessin like u said the float is taking on gas