raverx3m

After trans and tq fluid change(including new filter)
i found out that previous mechanic put in red fluid(it was reddish brown when i drained it)
car had very bad shudder and rpm fluctuation during light acceleration and rpm fluctuation while cruising.
after atf change it is much better but not completely gone

i noticed that the shudder and fluctuation is now within very narrow rpm range.
1500-2200 or so rpm.

i already replaced intake manifold with aftermarket one with good flaps.
previous owner supposedly replaced fuel pump recently per mechanic's recommendation.
plugs look good.

there are no misfire codes oe any other engine codes.

what else could cause this rpm fluctuation and shudder during acceleration

it is worse when going uphill in low rpm.
i dont feel it that much when accelerating harder.