MSD 6AL MISSFIRE???

All of a sudden out of the blue my engine is having longer cranking, some backfire, and will miss at load/slow drive speeds, then warm up and clean up. I have checked the following: went to new back up coil, changed dist cap, checked wires, changed plugs, checked compression, adjusted fuel pressure down about 1/2 lb to 7 psi , checked timing-dist hold down was slightly loose so i reset and tightened. The only component I can't test at home is the MSD 6al box. Has anybody had one go out like this? Its about 6 years old, but only about 3500 miles on it. I tried running it with the rpm module out, and no difference. Any ideas????

That's a new one on me.....Anytime I've seen an MSD go bad, it STAYED bad. Are you running any type of choke?

No chokes, a pair of Edelbrock 750's on top of a 871 blower, we removed the choke plates and all linkages to them. Plugs look good front to back, I pulled them and put in fresh, then compared the old to the last 2 other sets I've changed and no real differences. My Mallory dist. has a Petronix in it thats maybe a 6 months old tops, I don't think thats it either, but you never know. I haven't done any real changes to my combo in many years, its always run great, this is a weird one...

I had a 6AL go bad . It had a dead miss and a backfire. Changed everything including dist. & wires. At the end it was the Box. No warning. It's CRAZY but it happens.

I think tomorrow I will try unhooking the 6Al box and just run it on the coil and see what happens. I didn't find any vacuum leaks and the carbs seem ok, so I'll keep trying the process of elimination , hopefully I'll find it. I have an event in 9 days and I've got to get her ready... Thanks everybody for the input! Greg blown473