WHAT VEHICLE???
There are two main reasons for low pedal:
1. Air in the system. Makes for low-and-squishy pedal. If it's bad enough, the brakes just plain don't work.
2. Brakes not adjusted properly. Makes for low-and-firm pedal. Has to be REALLY bad to affect stopping power.
For fukk sakes, don't start welding until you're ABSOLUTELY sure there's no air and the brakes are properly adjusted. Front disc brakes shouldn't be a problem for adjustment, but rear drums can be, as can rear discs depending on the design.
IF (big IF) this is a 1500 with the ******, hateful Leading/Trailing Shoe rear brakes, you can about count on the shoes NOT being adjusted properly, because almost no one uses the park brake any more--and the park brake is required for the rear brakes to adjust. This is the style of rear drum with the adjuster ABOVE the axle shaft.
Using the park brake lifts the adjuster mechanism--then applying the service brake "triggers" the adjuster. So you have to kick the park brake, release it, then kick the service brake pedal. Then repeat about a dozen times. Be prepared to do it another dozen times--or pull the drums and adjust 'em by hand.
AND, any time the park brake is adjusted too tight, the service brake adjustment won't work properly. Always adjust the service brakes FIRST, and you will probably never need to adjust the park brake mechanism.