I just rebuilt my 04.5 allison 1000 with a merchant auto work series kit, their valve body with transgo installed and their single disk converter. When I'm at low rpm in 5th gear doing 50mph and I barely give it throttle I can feel it start slipping and then it limps. If I'm doing the same thing and I give it 50% throttle it will kick down and go. If I get on highway it's fine, all through the gears really nicely. If I get on it hard it holds but it feels a little weak, like it's slipping slightly. Any ideas what this could be?