First gear does not work in drive

When sitting still if you put the truck in drive and let off the brake the truck does not move even if you push on the gas. To get it to go I have to put the transmission into second gear only spot then when I get to 15 mph shift into drive and the rest of the gears work. I believe someone did work on the transmission before I owned it cause the shift lever wont go far enough to get the first gear only spot. I have put it up on jack stands put it in second gear only spot then went underneath and pushed on the shift linkage to get first and it worked the tires started spinning. The person who owned it before me said he got it stuck in a creek and that's when the problem started