'88 Carrera 3.2 shuddering problem

[Synchromesh]

I'm working on an '88 Targa that has been sitting for about 15 years. Lots of things have been done in the last few months. This is the engine stuff already finished:

1. replaced a bunch of oil and fuel lines
2. oil + filter
3. alternator belt (and removed AC compressor)
4. valve adjustment
5. O2 sensor
6. head temp sensor
7. adjust the 2 flywheel sensors with proper gapping
8. spark plugs and wires
9. dist rotor and cap
10. SW chip + solid state DME relay
11. Seafoam to clean the system first, now Chem Tool B60 to clean it further

Basically the engine runs relatively well but continues to have these issues:
1. idle is a bit high (usually at around 1000 rpm) and unstable with some dipping and hunting at times
2. not enough power
3. there's a noticeable shudder/lag in all gears between 1000 and 2500rpm. This is especially bad when shifting into gear from coasting

Any suggestions?
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'72 Super Beetle sunroof sedan