I took my truck to the mountains recently and I noticed that when I put the shifter into the first gear position, it won't catch. Instead of dropping down the first the transmission kicks into neutral. I thought this might be something that happens when you are going to fast for the gear except that it does it regardless of the speed I am travelling at when I down shift. The only way for me to put it into first gear is to stop and shift it down and then start off again. Does anyone have any suggestions before I put it in the shop? By the way, it's an automatic.

It could be your shift cable needs adjusted, it might not be going fully into the detent. At a stop there's no pressure on it so it might go in OK there. When you say it kicks it back into neutral, do you mean the actual shifter jumps all the way back to neutral or the trans just disengages? It's normal for them to not downshift if you're going above maybe 10 mph. You put them in first, they disengage, then drop in when you're going slow enough.