Your question has interesting information in it.
It sounds like you are saying that you bought the safari in 2004 from somebody and it had 54 k on the clock, so you drove it for the next 4 years and now it has 100k plus miles on it.
Ok, did you get tranny serviced anytime between the 54k to the 100k ?
Unable to determine from information provided under what conditions vehicle was operated.
Information not provide as to type,,model and duty cycle of previous chevy / gmc models for adequate comparison.
Possibility exists that trannsmission was not serviced often enough and has suffered premature failure.