Truck is in park but when I took it to the shop they said it showed I was in 3rd gear truck won't crank

Neutral safety switch located on driver side of trans. Could need adjustment or replacement. Two bolts attach it to trans. Clean and look close. When trans in neutral there is two little lines that will line up when it is adjusted correctly. Block wheels to Make sure it does not roll over you when your under it!

That guy ^^^

I've just encountered this exact problem. Cannot figure it out. Really need some help here. 2005 Silverado 1500hd. Cannot get power to the starter s post.

sounds like foster said its the neutral safty switch its located on the drivers side of the tranny it has two plugs going to it block the tires and put your truck in to park this is what i i did then go under your truck and find the lever the cable is hooked to undo the cable and by hand shift the lever towards the back of the truck that should be park once you do that look on the dash and see what gear is lit up if its not park then loosen the two bolts on the neutral safety switch give it a small turn until park is lit up on the dash once you get that tighten the bolts put the cable back on and your truck should start