Scott, I have heard that with a tighter converter when the rpm's get up around 800+ the truck will have a tendency to try to pull worse than stock. Maybe PB will chime in with his experiences. Not sure what my rpm's are now but mine acts the same way as yours. I am fairly certain I have a problem with the ABS and brakes. I know the brakes are worn but I can still set the parking brake and it won't pull thru it at an idle. Not so using the foot brake. It is taking more and more pressure to stop it and hold it at a stop sign and sometimes it will roll out after a short time. Going thru some of the old posts I think my ABS controller is going bad and just not applying brake like it should. The same could be happening with yours, or the converter is starting to weld itself, or there is a problem with the master cylinder, or possibly the proportioning valve is not working as it is supposed to.
As far as the master cylinder being a problem I don't buy it. On both my 92 2x4 and 91 4x4, when the brakes were functioning properly, they both stopped as well as any gas powered truck I have owned in the last 30 years. The wear and tear of sevral 100k and the intervening years have made a definite impact and it has to be mechanical. These trucks have to meet specifications for stopping when they are produced. It is inconceivable that a diesel truck would not have to meet the same specs for stopping as their gas counter part both from a safety and marketing stand point. Yes the brakes are undersized for what they are trying to stop, but, if it ain't stopping right there is a problem! Its not becuase of the type of MC, or the size of brakes, or whatever, its because something is worn and/or not functioning correctly. Finding which piece in which vehicle that is not up to par is where things get tedious, annoying, and sometimes expensive. For those of you that get the TDR magazine the last couple of issues had several excellent articles on brakes, braking, associated parts, and the possible effects of tampering and tuning.
Weight. This is the second post where somebody has made the comment the B series Cummins can't weight much more than a big block gasser. Come on!!!! The Cummins is not some light weight gasser V8 made for a light duty truck! This is a real diesel engine intended for a lot more than our trucks are ever capable of. The crank alone could function as an anchor for a fair sized boat! You have to take the head off with a fair sized cherry picker! I can pick up a bare 440 block and set in the box of my truck. If I tried that with a bare Cummins block I would be due for surgery where a perfect stranger with sharp instruments is waaaayyyyyy too close to parts of the body I consider precious. I am told the Cummins B tips the scales at a svelte 1100 lbs in our trucks. Now I know for a fact a 440 will not even come close to that. The truck engines are the heaviest and the 318/361 won't make that weight and I seriously doubt the 413 would either.
The glaring truth is we are using braking systems designed for a lot less weight and were marginal at best when new. Add the miles, the time, and in some cases the abuse, the fact we ain't dragging our feet to stop is a testament to the parts involved. The best way I have found aside from major expensive upgrades is to use good parts, use them often, and look for the problems with the existing pieces. Boring? Yes, but my truck stops.
My . 02
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