I haven't seen anyone do the switch back to Vetsulin. Once Neko switched to Lantus from Caninsulin (same thing but what it is called in the rest of the world), there was no going back.
A couple things have gone wrong with the switch to Lantus. First of all, you started back at 1 units Lantus when you were on 4 units of Vetsulin. Typically we'll switch to the same dose number, with maybe a bit lower for safety. So he should have started at around 3.5 units of Lantus. You still haven't even gotten up to the Vetsulin dose he was on before the switch.
I honestly think he just needs more Lantus. You also haven't really been following SLGS. With SLGS, you keep increasing every week of you aren't seeing nadirs in the 90-149 range. If you stick with a dose that is keeping him in high numbers for too long, glucose toxicity develops. That basically means his body gets used to those high numbers, and you have to go to an even higher dose to get over it.