5.7 Engine Knock

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.

Sound like your torque converter bolts are loose...check and tighten if necessary!