Otto, Just a thought but have you checked to make sure the exhaust heat flapper hasn't gotten stuck??? That could divert a continuous load of excess hot exhaust on your intake and from what I have read can add to the operating temps. Your temp increase under load is what brought this to mind.

~ Dan
1951 Chevy 3 window 3100
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"My Grandpa Carl's Truck and How it Became Mine"
1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver)
US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)