We have used single-lever faucets for 20 or 30 years in our stick houses, and now we have them in our motor home, too (shower, kitchen sink, bathroom sinks). We've never had a problem regulating temperature. I think AFChap may be right - there is something wrong with the faucet.
Not sure how your shower is set up. Ours has an access door to the back of the faucet, so it wouldn't be hard to change out. It would probably take two people - one to hold the faucet in the shower, and one to tighten the connections in the back..
2015 DRV Tradition 375KPS
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