Misfire on cylinder No. 3

no info generic answer if you have injectors most likely dirty or failing

head gasket blown or warped heador cracked head on engine

Here's a link for your misfire code. P0303 OBD II Trouble Code Cylinder 3 Misfire Detected

Misfire could be a number of things:
a) spark plugs - change them if used over 15K miles - inspect/regap.
b) spark plug wires - change them if over 15K miles - inspect
c) ECM (electronic control module) - test with HEI (high energy ignition) tester.

The vibrating tells me that the engine is running on less than its normal compliment of cylinders - the shaking is produced by the imbalance caused in the engine by one (or more) cylinder(s)
not firing at all.

The "Check Engine" light probably is coming on due the the misfire condition. Go to Pep Boys or
Advance Auto Pats, where they'll tell you (free) your codes causing the "Check Engine' light to be
lit - the code coming from your truck's computer will probably be one or more of:
P0300 - Random/Multiple Cylinder misfire detected
P0301 - Cylinder 1 misfire detected
P0302 - Cylinder 2 misfire detected
P0303 - Cylinder 3 misfire detected
P0304 - Cylinder 4 misfire detected
P0305 - Cylinder 5 misfire detected
P0306 - Cylinder 6 misfire detected
P0307 - Cylinder 7 misfire detected
P0308 - Cylinder 8 misfire detected
P0313 - Misfire detected with low fuel

Misfire could be a number of things:
a) spark plugs - change them if used over 15K miles - inspect/regap.
b) spark plug wires - change them if over 15K miles - inspect
c) ECM (electronic control module) - test with HEI (high energy ignition) tester.

The shaking tells me that the engine is running on less than its normal compliment of cylinders - the shaking is produced by the imbalance caused in the engine by one (or more) cylinder(s)
not firing at all.

The "Check Engine" light probably is coming on due the the misfire condition. Go to Pep Boys or
Advance Auto Pats, where they'll tell you (free) your codes causing the "Check Engine' light to be
lit - the code coming from your truck's computer will probably be one or more of:
P0300 - Random/Multiple Cylinder misfire detected
P0301 - Cylinder 1 misfire detected
P0302 - Cylinder 2 misfire detected
P0303 - Cylinder 3 misfire detected
P0304 - Cylinder 4 misfire detected
P0305 - Cylinder 5 misfire detected
P0306 - Cylinder 6 misfire detected
P0307 - Cylinder 7 misfire detected
P0308 - Cylinder 8 misfire detected
P0313 - Misfire detected with low fuel

could also be a bad coil or ignition wire

1.Plugs
2. Vacuum leak
3. Injector fault
4. High or low fuel pressure.
Thats the list of things to check.
This is a #3 cylinder misfire.
There is also TSB about #3 injector needing added heat protection. This could definitely be the cause. I start at plugs and go from there.
Hope this helps.
Thank you,
Lee

Check spark plug wires for corrosion

do a compression test then do a combustion pressure test if all good computer is questionable

misfire :-------- try checking your 02 sensors /fuel pump and filter.

for 51 cylinder misfire :---
Change the coil. Period. Very easy to remove from the vehicle if it's a 4 cyl. Follow that spark plug wire from the spark plug to the other end. What it's attached to you should replace
for 54 cylinder 5 misfire :---First you have to eliminate the most obvious problems, like spark plug and spark plug wire. If you replace those and you still have a misfire, then it's a good idea to look for a vacuum leak in the intake manifold