At one time I had a 93 FSM, didn't care for it, sold it. Too much clutter and gasser crap. Although it would be nice to have lol, just for the complete breakdown of about everything. In my library, I have a 74-88 Chiltons Dodge trucks, 78-93 Haynes Dodge trucks (nothing on 6BT), 89-91 Chilton (contains some 6bt info), 89 FSM (no diesel info), 89 FSM Diesel Supplement, and a Cummins Troubleshoot and Repair Manual, latest edition, would give the part number but it's out in the garage.
I have and have had intercooled and non-intercooled engines. It's a 5.9 B series Cummins for the most part, very little differences, at least that will matter in your case. My point is, the best manual I have found to use on ALL of them is the 89 FSM Diesel Supplement. I believe there is one for a 90 as well. Wasn't til 91 when Dodge included the diesel info into their FSM. The diesel supplement is written by Cummins, wipe your blank with what the retards at Dodge have to say lol. It's basically a Cummins Troubleshoot and Repair, Engine, and Shop Manual all in one. It contains info not included in my Cummins T&R manual. Complete tear down and rebuild info. In chassis, out of chassis etc. I highly recommend it. It usually can be found on ebay cheap as it's for the "early non-intercooled motors", not IC'd

. So the ding dongs looking for a shop manual for their 90-93 trucks see it and think it's useless to them.