Tups dying after shearing sounds like a tup with a full belly getting sheared? Our shearers prefer all sheep to have been hungered for a few hours. if not overnight, if poss.
Tups sold in excessively good condition (aka "show condition") then put to work can "melt".
Better if you can to buy direct from the breeder, and buy one "in his working clothes", ie., not fed up on high protein rations to look powerful in the ring.
Don't buy a cast tup, but some breeders will sell aged tups who would otherwise be coming onto his daughters. It's a good way to get good genetics into your flock, aged tups (usually 3-4 years old, maybe 5) cost a fraction of what he would have cost as a shearling.
Or, buy an unwethered lamb of the type you want in the store or fat ring. No guarantees, of course, but lots of people do this for home production.