I have always found this double pronunciation of Porsche interesting. I've always been in the "uh" camp, and it must come from the little bit of sports car racing that you could catch on TV in the late 60s / early 70s, because I sure wasn't around any Porsche owners in the middle of small town USA Indiana.......... but found it very confusing while living in LA listening to both pronunciations.
However, a couple of interesting observations - I have 2 well educated business colleagues that have had 911s, one even a
PCA racer and they both say Porsh. Drives me nuts, but I don't "correct" them. However, my brother also says Porsh, and I constantly correct him, openly and in front of others just because he's my "little" brother and "I have to".
When I seriously started looking at Porsches, 996s at the time, my first salesman was a German native, and what I noticed was that his "uh" was very subtle, and if you we're not expecting "uh" you wouldn't have picked it up, thinking he was saying Porsh.
And when Jay Leno was on Barrett Jackson, talking about his cars, he said Porsh as well. Although he only used the singular once that I noticed, when talking plural, he said Porsch Uhs.
....a recent lotto winner says he's going to go out an buy 2 fancy sports cars, and park one in front of his house, and one in back, because he always wanted his house to have a front Porsh and a back Porsh..... no, I didn't make that one up, just passing it along.