A very hard pedal with reduced braking is brake booster/vacuum related.
A soft pedal with reduced braking is a fluid leak or master cylinder issue.
If the pedal feels normal and you have reduced braking, I'd be looking at calipers.
Brake fluid should be almost water clear. The darker it is, the more contaminated it is. It should be flushed every 2 years or so.
Calipers should be rebuilt with OEM kits. If the pistons are corroded, replace them. They're still available new.
If the cylinder walls are corroded, then replace the calipers with OEM rebuilds.
All of the bits and pieces for the calipers are available new.
I have 2 sets of calipers that I rotate every 2 years or so. Both sets have been powder coated and get a complete rebuild with all new OEM parts when off the truck. Amsoil moly grease on everything.
Vacuum sealed and sitting on a shelf ready to be installed.