I have a 2003 s-10 vortec 4.3 4 X 4 checked brakes all good getting a SQUEEK from under the middle or truck weird any thoughts....

Braking or moving or sitting still?

slow moving speed thought I had done u-joints too sounds like that kind of squeek in gear moving slow

Does applying brake pedal or e brake make and change?
Recheck all u joints and double joints and carrier bearing.
Check brake pads and brake rotor slash shields.
If wheel covers make sure they are not squeaking.

ok pushed on the emergency brake today and the squeek got louder what could it be and do I do thank you very much in advance

E Brake shoes/pads worn out or metal piece or rock rubbing would be things to check.
And check e brake abels for stiching and wearing out e brake pads/shoes.
Check rear pads and e brake shoes.
If inside E brake shoe pull caliper an have a look.
Good Luck MT