Sometimes, but not always, it feels like my transmission is possibly slipping without really moving the vehicle along as it should. In other words, the engine sounds like it's being loaded per normal and the vehicle moves out, but slower than expected. It's almost like the transmission hasn't "hooked up" completely. Generally, when it's not having this issue, after leaning into the gas a good bit from a standing start I can feel the transmission seem to lock right into propulsion mode, and the vehicle jumps right into motion, well connected to the accelerator. The slippage--if that's what it is--often happens when in stop/start traffic. I think I can usually avoid the problem by keeping the transmission shifted into low.

I've checked the fluid level, it's on the money, vehicle hot in park, idling. Fluid looks clean, but I've never changed it in 5 years of ownership. Who knows if/when it was last changed. I haven't pulled the pan off yet to check/change the filter, but that's my plan. Figured I thought this out first, in case there's something I should do or check before or during the filter change.

Suppose to check in neutral idling not park

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63 Plymouth Valiant Wagon

does the engine seem to rev with the trans "lagging behind"?