Truck falls on face and Maf skewed right at 5krpm?

Have a 2004 Silverado SS with TSP 408 stroker low compression for boost. I retuned the truck after a shop had messed with it and ran great for about 8 months. Fuel trims dead on up to recently. Fuel trims have changed and right at 5k the MAF sensor reading skews right at 5krpms and truck falls on its face like someone just threw a rag in the intake. No tune changes had been made when this all happened. Found one valve spring broke but replaced spring and passed cylinder leak down test but said he had a problem before that happened. Fuel pump has been replaced with another Walbro. Swapped Maf sensors also with no change. Also acts sluggish for a short while after a wot pull and starts breaking up. I had good logs of the truck at the drag strip few weeks before all this happened and now fuel trims are different and bogging down at 5krpm but they are no good with new 3.0 scanner

What does floating a valve look like on a scanner? Also the passenger stft reading -90+ has to be scanner error it wasn't like that on 2.5