RPM's go high when driving but then go back to normal

COULD BE TPS (RPM) SENSOR,CLEAN THROTTLE BODY.

All the above is normal , except 2000rpm is a little high at idle . can be adjusted down to 1500rpm. the computer adjusts the engine speed . in drive the transmission loads up the engine idle drops to 1000rpm . in park engine unloaded rpm increase all normal.

Gauge problem ,bad stepper motor !
How to repair GM Instrument Cluster Speedometer Gauge Stepper

2 issues,
1: MPG, you failed to say MPG, 15mpg? or 39? is 39 low?
what MPG? you never said it?

2: rpm cruise. (what drive line, A/T M/T ?) what tranny?
first google hit , is this it? this yours?
engine: 1.5-litre 4-cylinder petrol, 75 kW/133 Nm
Transmissions: 5-speed manual, 4-speed automatic, FWD

3300 RPM in 5th and 100km
if you wish to now what is normal, find the final drive ratio, listed in the FSM. Id say this is normal. typical of tiny engines, with low torque.at lower RPMs.

if you have the A/T and IF the trannywere to slip, the TCM will infact throw DTC codes, telling you it did.
IS IT? (scan tools show you this fact as might that glowing CEL lamp on the dash, on driving.

RPM
my 1.6L spins 3000 RPM , at below tranny options valve counts.
54/59mph (104km/hr = 59) 5sp MT.
64.6 4sp A/T (goes fastest due to more aggressive OD + axle ratio is lower.)
56/.53 2sp A/T
see how drive line effects RPM? so will your cars options.

Sounds like the rear pads are worn out, your front brakes are keeping the truck from rolling. You need to have the high rpm checked for that 30-50 seconds as it is called the "cold start routine" and is meant to rev the engine for that time period. There may be an adjustment to keep it from over revving, check the specs for the rpm.

Even if you fix the rear brakes, the stress on the U-joints and differential or transmission is needless and can be fixed by limiting the high rpm in the "cold start cycle".

Check out related help links to troubleshoot these problem:----Click the link below:---Idles Fine but RPM jumps in drive mode?http://technoanswers.blogspot.in/2012/07/idles-fine-but-rpm-jumps-in-drive-mode.html
---------Mitsubishi Lancer rpm needle bounces?http://technoanswers.blogspot.in/2012/02/mitsubishi-lancer-rpm-needle-bounces.html
--------How to adjust rpm on 2009 dodge charger SRT8?

http://schematicsdiagram.blogspot.com/2011/12/how-to-adjust-rpm-on-2009-dodge-charger.html
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Engine cuts out at 3000 RPM?http://schematicsdiagram.blogspot.com/2011/12/engine-cuts-out-at-3000-rpm.html

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Cold start problem and vehicle shudder around 2500 to 3500 rpms
http://repairhelpcenter.blogspot.com/2012/10/cold-start-problem-and-vehicle-shudder.html

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High rpm in neutral? Inconsistant high RPM in neutral?http://technoanswers.blogspot.in/2012/02/high-rpm-in-neutral-inconsistant-high.html

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Jetski Sputters and Low RPM? http://whatisbyme.blogspot.in/2012/07/jetski-sputters-and-low-rpm.html

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Fuel Injection Problem And RPM suddenly increaseshttp://whatisbyme.blogspot.in/2012/07/fuel-injection-problem-and-rpm-suddenly.html

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2005 Toyota Highlander: Engine runs hard RPM below 3000?http://whatisbyme.blogspot.in/2012/05/2005-toyota-highlander-engine-runs-hard.html

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1987 Toyota Camry: RPM Drops going Up hills?http://whatisbyme.blogspot.in/2012/05/1987-toyota-camry-rpm-drops-going-up.html

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Cruise Control stops working, Excessive cranks to start the engine and RPM goes max 2500 http://whoisbyme.blogspot.in/2012/07/cruise-control-stops-workingexcessive.html

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1990 Toyota 4Runner: Engine cuts off when reaches 2000 RPM?

http://whatisbyme.blogspot.in/2012/05/1990-toyota-4runner-engine-cuts-off.html

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1999 Toyota Camry: Erratic stalling and high engine RPM at idle?

http://whatisbyme.blogspot.in/2012/05/1999-toyota-camry-erratic-stalling-and.html

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1995 Toyota LS: Misfire at idle or low RPMhttp://whatisbyme.blogspot.in/2012/04/1995-toyota-ls-misfire-at-idle-or-low.html

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Lexus RX: Tapping noise under Valve Cover At Low RPM?http://technoanswers.blogspot.in/2012/04/lexus-rx-tapping-noise-under-valve.html

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These will help.
Thanks.

Engine speed is determined from crank or cam sensor. You most likely have a cluster issue.

check your choke sensore

this is normal, if the idle wasn't high (about 2,500 RPM) the engine wopuld stall out until it warms up to normal temperature. If it is above 3000 RPM for more than a few seconds you have a problem.

check for a vacuum leak