1990 Other Ford Models hard starting

Had engine replaced in my 460 8 cylinder ford engine in my motor home. Runs good when it first starts up but when I stop the engine after it is warmed up it is very hard to get it to turn over. I installed double cables from battery to starter & has not helped. Wrapped starter with insulate material also underside of points under neath replaced. It just will not start like a normal engine. After 15 or so minutes it might start like it needs time to cool off. Also this is a Jasper engine replacement. Please help