that's great your dog walks good now, but if he's almost 5 months and you started using a prong collar a couple weeks ago get ready for negativity from the dog nazis.
a 35lb GSD is still small and developing, please don't pull on or run with him using a prong collar though.
We don't run him (period. unless he's fetching) or yank him when he's on the collar. The corrections are really light and subtle. I'd rather prong collar him than have him choke himself out on a flat collar. Thanks though! Everyone has their opinions, I suppose.