I have a 2008 Silverado 1500 2x4, 150k on original motor and 50k on reconstructed engine for a total of 200k. Transmission hasn't been swapped or reconstructed it's in its original state. My truck started leaking transmission oil through the transmission vent hose, and struggles to change gears. On a complete stop Rpm reaches and stays between 4rpm and 5rpm until I reach final gear and then it drops down to 3rpm and stays at least at 3rpm for the remainder of the ride. Engine service light does not turn on and no message lights up inside dash. I have replaced the transmission oil and filter a few months ago, and it's not overfilling with transmission fluid