Gear oil is foamy! WHY ?

Hello. at my Dodge RAM 1500 1995 I checked the gear oil today and it was very foamy. What’s going on there? the car drives everyday and did not have any problems of its own. Except one: If it is cold and I go off and then after a short distance (about 500m) stop jumps the jump I believe on N or so when driving there is a back and the gear is back in. The rest of the ride then nothing unusual happens. That was also the reason why I opened the car. Thank you in advance Holger