Well good for you, wanting to make your curry your way.
And your way, the lamb is bland and doesnt have a good curry flavour., so I guess its either carry on your way or go someone elses!!
Everyone has given good advice on how to get more flavour into the dish . I agree that the curry powder/spices MUST be fried in oil first ( either with onions or the lamb) to get maximum flavour. Adding the powder or spices to a liquid just will not provide depth of flavour. And BTW, frying off batches of your lamb before cooking will give you a 100% improved dish. An hour to prep 2.5 lbs??? Are you boning lamb with a butter knife??
Good luck with your curry.