When your film is uneven,the developer is getting exhausted, follow the replenishment instructions from Kodak. You are also finding your negs flat, increase the temperature of the developer to shorten your development time, agitate ten seconds for every minute of development. With Tmax 100 or 400, use a yellow number 8 filter on your lens, this really helps with the contrast. Uneven negatives can also be caused by inadequate agitation, so focus on being consistent with this aspect of development.