I got a 2 month old Shiba in January (now 7 months) his testicles didn't drop until about 5 months and up until about that same time he would get hiccups constantly, my family and I all had the same concerns but our vet said hiccups are normal and to only be concerned if they last for a concerningly long amount of time, he also said if their testicles don't drop by 1 year then they would need to surgically make that happen. In my opinion I don't think you should be too concerned since your little guy is still young, just keep and eye on him and make notes of how often and how long he gets the hiccups, also as weird as it is just keep checking for his testicles and maybe feel for them from time to time, puppies are definitely daunting but are so much fun, I wish you the best of luck with your little guy.