97 lesabre code p1870

when on highway or interstate the car will shudder intermittently, usually after being driven about 20 miles it will start, check engine light doesn't always come on but when it does, code p1870 comes up, i have just changed the fluid and filter, it isn't as bad as it was but is still doing it, is the converter bad or is there something else i can try? thanks

The most common reason is the bore in the valve body for the TCC valve wears and causes the tcc to slip, but there are other causes also, if you do a site and google search there is a lot of info out there on this common GM code.