IMHO, DTT. The big difference is BD uses a milled stator, and DTT uses a custom built stator. The DTT is more efficient at all rpm levels.
You should speak to Bill K.
www.dieseltrans.com
I put mine in a week ago, and couldn't be happier. I was very concerned at first about the modifications. However, I took it to a shop that installs BD, and the tech remarked how easy it was to do the DTT.
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1999 2500 4x4, auto, 3. 54 LS, HD241, Quad cab SLT, Blk Sport Pkg, 16x8 Eagles, 285 Bridgestone AT, Amsoil, 80/100w lights, Valentine One, DTT TC/vb, DD2's, DD TTPM, Isspro gauges.
1992 SC400
1978 Mooney 201 IFR