[oil pan 4]

I am not sure what year GM switched over to DB4, but it was around 1994.
I stay as far a way as possible from the DB4.
The DB4 is toxic, just don't waste your time with it.
When I built up my chevy diesel I used all the best parts from 1984 to 2002. Just because something is new doesn't mean its better. The 6.2L and 6.5L serries one of the best examples of this.

Any half ton GM truck from about 1956 to 2000 or 2002 offered a SBC or BBC engine. All camaros up to about 1994 offered an SBC and a few other cars offered SBC over they years.

The TH700R4 is the most common economy transmission.
I have towed with my TH700R4 and it seems to do ok.
The TH400 or 4L80E is also popular but its a big some what inefficient tow transmission, its also the popular 4x4 transmission.
There is a guy over on dieselplace.com that was working on putting a 6-speed T56 transmission in a 6.2L.
I don't know if anyone has ever tried towing with a T65, its a high performance car transmission.
The 4-speed and 5-speed manual transmissions that originally came with the 6.2L and 6.5L engines are pretty rare.

Aftermarket turbocharged 2wd chevy blazers with 5 speed manual transmissions have been known to get nearly 30mpg. In a car or small pickup I think a properly setup chevy diesel could get 35mpg.

Originally I wanted to get a diesel blazer but they are pretty rare and I setteled for the suburban.
For a little less MPG I ended up with a much more capable work vehicle. I like the suburban because it can hold 8 foot 2x4's and 4x8 foot sheets of sheet rock or plywood and keep them out of the weather. It can take up to 12 foot lengths of wood no problem, they just hang out the back a few feet.

The 6.2L and 6.5L engies are also very popular for light duty marine build ups, but that is a whole nother world.