Answer: I have notice two things that cause my pepper plants to grow slowly: cooler than normal temperatures, and soil that is too wet. Of course too dry and low fertility levels in the soil can also result in poor growth. However, your information indicates that these causes are unlikely.
Dig down a few inches and see if the soil may be staying too moist. Otherwise, my only suggestion is to wait and keep doing the right things. One thing many years of gardening have taught me is that each year is different. Plants may thrive one year and struggle the next. I guess that is part of the challenge of gardening.
Good luck with those peppers. Hope they pull out of this soon!
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