I feed both of mine Iams and it works great for them. Others will probably have better suggestions for higher quality foods but our dogs do fine on Iams so that's what we feed them. They both have shiny coats and abundant (!!!) energy.
What exactly (brand of food) are you giving your pup and how often are you feeding him?
Here's what we did! We had our two pups at 9 weeks and my breeder had been feeding them (4 times a day) starting with porridge and goats' milk for breakfast then lunch, tea and supper with what he called 'black tripe' (unbleached tripe) and Eukanuba puppy food (for large breeds), which he moistened with warm water as it was easier for them to eat with puppy teeth.
We continued with Eukanuba puppy, moistening it with warm water for a few minutes and used tins of 'Butchers Tripe' and mixed small amounts of this with the Eukanuba and continued 4 times a day until they were around 5/6 months and then we fed the Eukanuba puppy dry as they got bigger. We fed the same amount of food divided up into three meals a day for several months (forget exactly).
At around 12 months we changed to adult Eukanuba for large breeds (IAMS is almost the same I think) and fed them morning and teatime with the Eukanuba with a small amount of tinned Butchers tripe mixed in as wel. Also a treat at lunchtime as they continued to look for something so it was often a few pieces of dried food/small treats inside a treat ball that they enjoyed pushing around the kitchen and hall and kept them occupied as the treats fell out for them or a couple of dog chews etc.
I hope this helps you. Ours have thrived and I hope yours will too.
PS: A good breeder will do what mine did which was to give us a bag of dog food and lots of typed up advice sheets, but we've had many years of Basset ownership so could cope OK with feeding etc!