Changing Puppy food?

Question
I just received my 9 week old, male, rat terrier pup on Christmas eve (True). He came via Delta Pets1st from Indiana to Rhode Island. When I picked him up from the airport he seemed fine he didn't even wet up the kennel, he went on a puppy pad the was folded in the corner. The breeder advised me that he was on Diamond puppy food and sent some w/ him. That night and morning I noticed he wasn't eating that much. He was eating and he wasn't sick, he just didn't seem very interested in his food. When I went to the vet they gave me Science Diet puppy food, and told me to begin weaning him off the Diamond food ASAP, but very slowly so his digestive system wasn't affected. They told me Diamond had a mold problem last year and a lot of puppies died.
  Well the 1st day of mixing the food I put 1/3 science diet, 2/3 Diamond. True only ate the science diet very happily. He finished it all and was begging for more. Later on that day I mixed the food exactly the same but he only eats the new food. I went on like this for 2 days, he never got sick. On the 3rd day I only gave him the Science Diet, he is still fine no problems at all. Do you think he could still get sick? Also I bought a 40lb bag of chicken soup for the puppy lover's soul puppy food, after doing a lot of research on good puppy food. Could he get sick when I start to wean him off the Science Diet, since he might like that food more as well?

One other question:
What is the best way to teach him his name? I've tried calling him to me w/ treats, but he follows me all the time so I don't think he is getting the concept.

I'm not sure what to do, but I would like your input on the best way to switch w/o True reacting?

Answer
Hello, Yes i would get him off the diamond thou I've never heard of it if its a quality vet you have and knows what he is talking about or she is talking about(my vet is a lady...shes very smart and anwsers everything I ask her in great detail). If there was a problem with the food before or it doesnt seem high quaility change it, if the puppy is enjoying the other food let him eat that daily until he is on adult food, Science diet isnt as hiugh quaility as puppy food comes.... I've heard of the chicken for the soul is a good food thou it isnt sold near me so I havent a clue whats in it...dont mix three foods together I dont even reccomend trying the new food right now you've Just changed his diet doing so right away again might cause throw up episodes or frothy slime vomit...its gross trust me lol. Wait for a few weeks and swich foods to the one you plan to keep him on for his puppy months....make sure if you change from science diet that teh food is a small breed puppy food or at the lest a puppy food, he will need to be cahnged from the puppy food to adult food at 6-12 months...I always swich my puppies at 5/6 months to adult fod its much easier when you have other dogs in the house...puppy food aids in growth on adult food small breed puppies are nearly full grown or full grown at 6 months...the dog grows the same size but slower swhich in the case of large dogs could be a big benifit. To make things simple don't swich foods too offen my dogs have found a food they like and have been eating it for the past year with pleasur, don't spoil small breeds such as "True" on canned of moist foods its bad for the teeth and will cause tooth decay in the future, Try get True used to hard biscuts such as milk bones....there are other bones of better quaility in the same texture...the hard bones will help keep tartar off teeth small dogs mainly toy breeds are picky eaters so far so good with True, best of luck with your new puppy if you have any more questions feel free to ask.

Oh almost forgot for name training I just say the puppies name whenever I want her to or him to come to me...snap your fingers clap your hands make kissing sounds and call his name he will come flying...give a few weeks and the puppy will know its name...forget nicknames at this time or the pup will get confused....call True come here True and whisle or whatever you want to use and make hand signals for him to come to you make your voice high and sqeaky over excited puppies respond well to this for this subeject.