Depends on what you call a long grade and also depends on what you call
"painfully slow".

On a 6-7% grade I downshift to third and cruise up at around 45mph.  That,
to me, is not painfully slow, though others more used to American big blocks
would mostly disagree.  My old '62 40hp bus would climb the same grades at
around 23 mph in second gear.

Overheating has never been a problem in any of my vans unless there was a
"situation" in the cooling system.

Karl Wolz

Respectfully, I would say that depends on how you define "long grades,"
and also how you define "handle it fine."  My 2.1 camper handles long
grades fine, but I drive slowly relative to other traffic, and it drops
speed on long grades.  I do have to downshift.  It is well tuned.   A
long grade in one part of the country may be a mile of 3%, but no one
who drives in truly mountainous country would consider it so.  If you
drive a 2.1 in the mountains, you will drive slowly relative to ordinary
traffic, or you won't drive.

David McNeely