I have a Chevy Express 2500 HD with a 5.7L and 4L80E Trans. My Tranny was having a mayor vibration whne shifting gears and then I lost the reverse. I replace the tranny last week and know I hear a loud bottom engine knock when I first start the Van the noise lessens however when I accelerate you can hear it. The motor does not smoke and it feels strong when you drive it. The engine has about 75 miles on it. Any suggestions.