Deadlift Programming

5’10" 31 yo, ~198lb body weight
I started LP at 170lb BW with very small weights and have made it to

Squat 345x5
Bench 215x3
Deadlift 385x5
Press 135x5

My squat is going fairly well with backoff sets, but my deadlift has been…interesting. I ran my deadlift LP to 375 and then had issues increasing past this point. During the end of LP I trained DL once per week (Friday) because of recovery and have since added in a medium day with 3x5 that started around 275lbs. It seemed to help for the first week or two. I just completed 390x4 the prior week so I was going to attempt 390 once again. I did 315 3x5 Tuesday and tried for a 390x5 on Friday which resulted in 355 @9? and then some backoff work to get volume. It felt like I had not recovered. I’m assuming I just need to get accustomed to volume, but is there something extremely flawed with my programming?

If you were programmed to hit 390x5 and only hit 355 for a hard single, then you weren’t adequately recovered for that session, and doing extra “backoff work to get volume” was burying you even deeper in the hole on that particular day. Not the best choice in the context of the LP.

It sounds like you should probably just move on to intermediate-style programming.