mass air flow sensor
the rpms should rise and then drop no more then 500 rpms when the fan on the radiator turns on and then off.
When your RPMs get down to 1000, you take it out of gear, press the accelerator to tach the motor up to 1500 RPMs, and drop down into the next lowest gear. Assuming you're operating this truck in North America, your transmission will either be an Eaton-Fuller or Spicer 10 speed unsynchronised transmission, and you must tach up to motor to compensate for the lack of a synchroniser gear in the transmission. If you drop your RPMs down to 700 - 800 before downshifting, you can skip a gear in downshifting, and downshift two gears.
check your mass air flow sensor located near the air intake
You can do it at pretty much any RPMs, so long as your timing is right. I can hit gears upshifting at 1300 or 1900 RPMs with no problem. What the ideal shift range is will depend on the engine. As a general rule of thumb, most people say 1400 - 1600 RPMs... personally, I like to shift a bit higher, and drop back down into the powerband when I go into the next gear, so that the engine isn't as prone to bogging down.
If you don't know how to downshift (and upshift) and unsynchronised manual progressive shift transmission, you really need to go to a truck driving school. You're not going to learn how simply by read about it. In school, they'll teach you to drop the RPMs down to 1000, pop it into neutral, kick the accelerator to 1500 RPMs, then drop it into the next gear. It might look simple enough on paper, but you're not going to get this down without some hands-on experience.
Drop your RPMs to 900 - 1000, take it out of gear, rev the motor up to 1500 RPMs, put it into the next gear down - the same way you would with a nine or a ten speed - for your major shifting motions. If you're just looking to drop to the bottom side of a gear, you simply flip the side button back, and give the accelerator a little tap. If you wanted to downshift from, say, 12th to 11th gear, you'd flip the side button forward, then downshift into the next hole the same way you would if it were a nine speed.
If your 1992 Voyager does not seem to drop into the proper RPMs so that you are running at 5000 RPMs at 65 miles per hour, the timing belt might need adjusted. It can also indicate the idle is set too high.
They're unsynchronised progressive shift transmissions. Unlike the manual transmissions found in regular passenger cars, which are synchronised, you don't just simply take these out of gear and put them in the next gear up. To upshift, you would get up to your desired RPMs (usually between 1300 - 1500), then take it out of gear. You would then put it into the next gear up when the RPMs wind down to 700 or so. Downshifting is a little more complicated. Here, you would wait until the RPMs went down to between 900 - 1000. You would then take it out of gear, tach the motor up to 1500 while out of gear, and drop it into the next gear down at 1500 RPMs. For road tests, you'll be required to use the clutch with each shifting motion - this is called double clutching. It is possible to upshift and downshift without using the clutch at all, but, if you haven't gotten it down properly, it could end up causing serious damage to the transmission.
If it's cold outside, it's because ECU use ambient temperature sensor and coolant sensor to manage RPMs. After you start the car the coolant temperature is low and ECU sets RPMs very high, when it gets warm RPMs drop down until engine reaches operating temperature.
If you drop a grand piano down a mine shaft you would get a flat minor.
If you drop a grand piano down a mine shaft you would get a flat minor.
There is no way of telling, all monsters drop at random, if there were certain kills you have to get, the game would hardly be any fun.