strange neutral problem

[jayzauto]

ok i have a 91 4wd 4.0 auto. I'm not sure what tranny i have. i recently did a 4.0 swop out of a 97 xj and ever scents then it occasionally acts like it bumps itsself into neutral i rev it up a bit and it knocks its self back into gear.  it only does it when i come to a compete stop and it seem the harder i brake the more likely it is to do it. any idea what this is? I don't think its a tranny problem because wouldnt it mess up in other gears?

[HOrnbrod]

Check your tranny fluid; level and condition.

[CJ's 89 MJ]

X2. If that doesn't solve recommend new transmission filter.