Aircraft taxy characteristics on grass

Hi all. Over the holiday I loaded up FSG North America, GE Pro, UT USA, Portland and Rhode Island - and somewhere in there I noticed my aircraft are now taxying (on the pan/concrete taxyways) as though they are on grass: i.e. they "lope": the nose goes up and down, and there is visible dirt being thrown up from the gear. It's not so noticable in a taildragger, but it's still there, and really noticeable in the 727. It applies to all airports I've tried. It seems to be loading the wrong "whatsitcalled", but I don't know where to start looking. Thanks for any assistance.pj