I have a 1987 D150 with a 318. I have been slowly diagnosing problems and repairing them. I've been having problems with starting the truck and it running rough. I had to adjust the timing to its proper 8° BTC etc. I also discovered at that time that the distributor was electrically controlled and the engine had a SCC (Spark Control Computer) behind the battery. I replaced the 28yr old SCC with a new one and solved most of my issues. However I now have a new one. The torque converter will no longer engage. It shifts 1st, 2nd, and 3rd just fine, but that's all. Before I replaced the SCC, the torque converter would engage.

Any ideas where to start looking?

Thanks.