I am new to diesels and bought a used 2004.5 lly with 30,000 miles on it. The gentleman I bought it from used it to haul livestock trailers and had a predator on it. He also told me that it had a few tranny mods to help with pulling, and me not knowing anything at that point didnt think to ask what had been done. Well I have slowly been building it up to pull in the county fairs with and to this point havent even had to think about the trans. I had a van aaken 180hp hot stacked with a quadzilla 135hp and that didnt phase the trans at all. Well the other day I got Mcrats race tune and put it on then tiik it for a test run. I opened it up and the first couple of times it ran very verygood, no probs. Last night I did it again after adding a modified cp3 pump since I ran out of rail pressure a couple of times, this time I got a check engine light and it started acting funny. Wouldnt shift into drive for me. I checked the coded and got (if I remember right) p0706-silenoid A stuck open, and low fuel rail pressure during power enrichment. I understand the low fuel pressure but what is the silenoid A stuck open, and how bad is that. I dont know how modded up the tranny really is but till now its been OK and I cant ask the guy I bought it from due to him passinf away recently. If anyone knows what that code is and how bad it is please tell me, and also how modded do you think the tranny really is. Thanks

No real way of telling except if you were to drop the pan and see if it has Transgo valves in it.

Most likely he simply put Bullydog valves in it which don't do much of anything.

Since your competing I suggest just getting a Suncoast kit and a TC and be done with it.

Your rail pressure problems might just be that u need a shim kit from ppe they or only 10 dollars and are well worth the money