99 Isuzu Amigo Shifting Hard and indicatior light problems

My wife has a 99 Amigo v-6 with 4 wheel drive. In the last 2 months she has had an issue with the indicator light not showing it in drive
and not going into gear in the morning. Now it has done that and when the car down shifts into 1st gear it shifts real hard and makes a loud chunck sound. it was intermitant at first and now is happening more often. The car only has 39 K on it. Is this an e-lectrical issue or a transmission issue. The check engion light is not on FYI
Tha car has had the intake manifold replaced 2 years ago and is idling high in the mornings - expsecial whenit is cold. Up to 1500 RPMS.? Any suggestions. I did chgange the TPS but noticed the sensor on the other side of the air intake hose is dity. Air control sensor?
Help Please
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