There should be a "sprint mode" that is 1.x normal speed (where x = your agi. 10 agi would net double speed.) with the following conditions.
Can only sprint for 10 sec times your endurance. And must walk at normal speed for (30 minus triple your endurance) seconds to recover. Ergo, 10 endurance characters could sprint forever.
All weapons are unequipped or holstered while sprinting.
Sprinting is noisy. Will attract a lot of attention if running near enemies.
Cannot sprint if over encumbered.
Sprinting too much will give you a temporary -1 charisma penalty called "Sweaty"
*** huge caveat *** just throwing our numbers for examples. Actual % could vary wildly pending tests.