1990 Chevrolet Suburban Starting problems

The parts you listed won't cause these symptoms. The ignition coil doesn't even do anything until the engine is cranking. The goal is to get the problem to occur so you can diagnose it. Start by turning on the head lights and observing the brightness. That will insure some current is trying to flow from the battery and will make voltage measurements more accurate.

Measure the battery voltage first. You will find 12.6 volts if it is fully charged. If it's around 12.2 volts it is okay but discharged. If you find closer to 11 volts or less it has a shorted cell and must be replaced.

If the battery is fully charged, move the negative meter probe to the end of the smaller battery wire to where it bolts to the body and measure there. The voltage should be the same. Check that bolt to be sure it's tight. Move the positive meter probe from the battery to where the smaller wire bolts to the under-hood fuse box. The voltage should be the same there too. You're looking for the first place the voltage drops. That will be the point of the bad connection that must be cleaned and tightened.

The pickup assembly doesn't even do anything until the engine is cranking. It will not cause a failure to crank.

I'm not a fan of removing parts for testing. Almost any starter will test good off the engine, even those with bad brushes or bearings, because there's no load on it. A free-spinning starter motor will draw as little as 50 amps. You need to test it under load when it will need to draw up to 300 amps to get started, and around 150 - 200 to keep cranking. That's where bad brushes will show up.

Generators need to be tested for full-load output current and "ripple" voltage. That will identify one bad diode of the six. With one bad diode the generator will only develop a maximum of exactly one third of its design rating and that's not enough to meet the demands of the electrical system under all conditions. The battery will have to make up the difference until it runs down. That's why I had you measure the battery voltage first. The test benches at auto parts stores aren't strong enough to run a generator at full load. They can only measure the output voltage, (electrical pressure). It has to be on the car to measure maximum current, (electrical flow). In most cases when the maximum current is low due to a bad diode the output voltage will still be near perfect, so you can get a false good result on a test bench.

Regardless of these test results, I'm still thinking about the symptoms that point to two different problems, but presumably related. Slow cranking points to a discharged battery or a bad connection / frayed battery cable. No-crank with no sound from the starter suggests a problem in a circuit other than the starter circuit and battery cables. Most commonly the neutral safety switch would be the main suspect. The no-crank can be partially diagnosed from the starter relay but you have to do it while that problem is occurring.