Allison Trans shifting problems

[BigHartz]

I have a 1995 Spartan 5.9L Cummins Allison 6-spd pusher. My problem is rough up shifts. It bucks as if the engine was stalling then shifts hard into the next higher gear. Test driving it yesterday I noticed that the tach would actually drop from 2000rpm to 1000rpm a couple times then shift to the next higher gear at about 1500rpm. After several of these shifts I believe I actually saw the shift indicator go from 1st to 3rd than to 2nd. It will shift this way when up shifting through most all the gears. I noted also that the down shifts are some times very hard and abrupt. When in 6th the converter lockup works correctly and trans will downshift on grades properly. What might be going on? Is there a way I can get the trouble codes without a scanner? Thanks Dave Hartz