Our place is 17 years old and apparently no one had cleaned out the dryer vent before now. It was extremely clogged up. While the vent was clogged, the dyer worked great - dried an average load in 45-60 min. Ever since we cleaned out the vent it takes 4 hours to dry a load. Coincidence? What could cause this? Any tips of suggestions greatly appreciated. Thank you
After cleaning the dryer vent you should be seeing shorter drying times per load. A restricted dryer vent limit's (reduces) the amount of warm, moist air being exhausted; slowing drying time. As already mentioned check again for lint blockage. If the thermostat is defective it will not fully heat-up. Put your hand on the exhaust duct; it should be warm. Dryers employ a blower to circulate the warmed air. If the blower's drive pulley is loose it can't blow air. If the dryer uses electricity to dry clothes the heating element could be damaged.
I will second the theory that the vent, while caked with lint and restricted, was never fully obstructed anywhere; by clearing most of the vent, you've inadvertently created a complete blockage somewhere that your cleaning tools didn't reach.
To diagnose this, start the dryer on any cycle (air fluff is fine), then check the airflow at the exhaust vent. If there is none, or very little, you still have a blockage, or else your cleaning efforts have poked a hole or disconnected a length of the dryer vent.
First, make sure you haven't damaged anything, by visually inspecting as much of the dryer line as you can access. Plastic or foil dryer vent line is practically worthless; it'll become very brittle with the constant heat of the dryer exhaust and will get torn to shreds by most of the available vent cleaning tools. If this has happened you'll have to replace it. Even semi-rigid aluminum ducting can relatively easily be damaged by cleaning tools; these tools are designed for use with rigid galvanized duct line.
Assuming you haven't damaged anything, the remaining problem is a leftover blockage. Repeat the vent cleaning, making sure to run the tool to the maximum depth you can reach (most flex-rod type systems will extend to the maximum code-compliant length for the vent itself). If it's possible, try running your cleaning tool in from the outside, with the dryer running; this will give you a pretty obvious clue if and when you clear the obstruction (you'll be showered in lint when the brush breaks through and the dryer's airflow clears out the loosened obstructing debris). Also check the dryer itself; a substantial length of exhaust venting is within the dryer itself, along with some tight corners which are often the first to fill up with the gunk that the lint screen doesn't catch.
If the airflow is good but the drying time is still terrible, it's likely the dryer's heating system; with the dryer set to high heat, make sure the exhaust air feels nice and hot after a couple of minutes. If that isn't happening, the restricted airflow through the clogged vent may have tripped a thermal fuse or caused a short in the heating coil very close to the time you cleared the vents. Those problems also have DIY solutions but will require more information, and you would have been more likely to see a severe dropoff in drying effectiveness before you cleaned the vents.
If the heat's good and the vent's clear, it's down to user error; make sure you're not overloading the dryer with clothes (the best advice I can give starts way back when sorting clothes; never put more than one loose, level basketful of clothes in the washer even if the tub looks like it can take more), and if your dryer has a dryness sensor system, make sure the sensor's clean and that you fill the dryer with clothes of similar material; a cotton terrycloth towel in a load of synthetic fabrics will never dry completely before the sensor determines the majority of the load is done.