Glad to hear it! A milestone accomplishment! As to the late, harsh shifting, I concur. Vacuum to the modulator valve likely has been compromised or the modulator valve is faulty. Check the entire length of the steel vacuum line for perforations, paying particular attention to the rubber hose ends that connect the line to the vacuum source and the modulator valve. It is common for the rubber connectors to soften and become spongy over time or split and leak. Disconnect the vacuum line from the modulator valve in the transmission and spin the valve so that the vacuum nipple is oriented downward. If ATF collects and drips from the nipple the modulator diaphragm is ruptured; replace the modulator valve. Typically, the valve will be color-coded with a dab of paint on the end of the can. The replacement valve should be color-coded the same to maintain original shift calibration. In addition, spray around the intake manifold, PCV valve hose, EGR base and TBI base using some aerosol carburetor cleaner (e.g., Berrymans B12) to determine whether there are miscellaneous vacuum leaks. Temporarily pinch off the vacuum hose to the brake power booster to determine whether there is any momentary change in idle quality. The power booster vacuum hose should be thick wall 11/32" line specific to booster applications. If 3/8" PCV vacuum hose has been substituted for the correct booster hose, replace it.
Another cause of shift errors is a sticky governor valve.